Gia Petriashvili

In this letter, we report the results of phototunable lasing in dye-doped cholesteric liquid crystals (DD–CLC). Photoexcitation of DD–CLC films gives rise to laser emission in the violet-UV range. Control of the structure of the chiral dopant driven by UV phototransformation is exploited in order to obtain a permanent variation of the cholesteric pitch. Laser emission wavelength tuning, by means of photoinduced shifting of the selective reflection band of the cholesteric liquid crystals is established. A tuning interval of about 35 nm, in the wavelength range of 385–415 nm, is observed.

Tuning of a dye-doped cholesteric liquid crystal mirrorless laser in the violet– ultraviolet wavelength range is achieved using two different strategies for controlling the periodicity of the cholesteric helical structures. Both methods are shown produce a shift of the lasing wavelength by 30–40 nm, and smooth variation of the helical pitch can be achieved.

For the first time the photooptic effect in induced cholesteric mixtures using photosensitive nematic host has been observed. The changes of the pitch (color) and optical anisotropy (Δn) and also cholesteric-isotropic phase transition have been studied. Potential applications of these systems are color filters, UV image recording, UV sensors, and optical data processing systems.

LCDs based on a luminescent dichroic-dye-doped non-absorbing cholesteric LC with positive dielectric anisotropy is proposed. In the initial state, the orientation of the dye molecules provides effective light absorption and irradiation. By applying an electric field to the cell, the absorption and thus the luminescence is absent. A two-color luminescence could be achieved by sandwiching two cells: the upper cell consists of a cholesteric LC with two dyes (sensitizer and emitter) and is used with an applied voltage (active cell); the lower cell consists of a cholesteric LC doped with one dye and works without applying a voltage (passive cell). The performance characteristics of luminescent dye-doped cholesteric-LCDs were investigated.

We report the observation of laser emission from a luminescent dye-doped cholesteric liquid crystal (CLC) excited by another dye-doped CLC laser. The idea is based on the cascade of two CLC cells containing two different dyes where the emission band of the first overlaps the absorption band of the second. This system of low threshold mirrorless lasers emphasizes the main advantages of these organic materials for lasing applications and identifies a simple laser device. Preliminary characterizations of these CLC laser systems produce evidence of remarkable features that suggest fascinating developments. The main aspects are related to the wavelength tunability of the laser emission and to the miniaturization of the device.

It has been shown that UV radiation can produce observable color changes in induced cholesteric systems (nematic + optically active dopant) additionally doped with ergosterol (provitamin D2). The effect is based on the photoinduced conversion of ergosterol into vitamin D2, which has the opposite sign of its helical twisting power. The observed shifts of the selective reflection peaks (more then 100 nm after 10 min of UV irradiation) allow both instrumental and visual monitoring of biologically active UV radiation.

Quasicontinuous tuning of a dye doped cholesteric liquid crystal (CLC) mirrorless laser in the ultraviolet-visible wavelength range is demonstrated using a single original device based on CLC as resonator and several resonant dyes. The thought is to combine the CLC pitch gradient and the distribution of different dyes. In the same cell, six dyes are combined in order to nearly cover the whole wavelength range from ultraviolet (370 nm) to red (680 nm). Some of the used dyes work as emitter, while others work in the Förster regime to decouple the excitation and emission processes. The relevant aspect of the device is that a simple translation of the cell respect to the same pump beam enables fine tuning of the laser wavelength in almost all the visible range, up to the ultraviolet.

A new class of photoactive chiral liquid crystals based on a photoactive nematic host material and a photoinactive chiral dopant was utilized to investigate the behavior of the blues phases when trans-cis isomerization is induced. While the general behavior follows what has been observed in the cholesteric phase, the sensitivity of the blue phases to external parameters causes different behavior when these systems are exposed to UV radiation. The results for four different mixtures are reported and include (1) modulation of the blue phase selective reflection wavelength with low levels of UV and visible light, (2) conversion of one blue phase to another upon exposure to UV light, and (3) induction of blue phases due to UV irradiation when no blue phases are stable beforehand. It is also noted that the supercooled blue phase behaves differently from the other blue phases. All of these results can be understood qualitatively from the ratio of non-nematogenic cis isomers to nematogenic trans isomers and chiral molecules.

Shifts of selective reflection peaks under UV irradiation (which can be observed as color changes) are reported for induced cholesteric systems (nematic + optically active dopant) additionally doped with ergosterol (provitamin D2) or 7-dehydrocholesterol (provitamin D3). the effect is based on the photoinduced conversion of ergosterol into vitamin D2, and 7-dehydrocholesterol into vitamin D3, with the vitamins and provitamins having opposite signs of their helical twisting power. The observed shifts of the selective reflection peaks (more than 190 nm after 45 min of UV irradiation) allow both instrumental and visual monitoring of biologically active UV radiation.

Three photosensitive cholesteric liquid crystal mixtures have been investigated as UV sensors. Each of them is sensitive to a well definite part of the solar UV radiation spectrum, the UV A or the UV B or the UV C range, with suitable absorption spectra. The photosensitive elements in the mixtures are either photoisomerizable nematic hosts or photoisomerizable optically active dopants. The selective reflection peaks of these cholesteric mixtures are in the visible part of the light spectrum. The UV exposure changes the cholesteric pitch and hence the position of the selective reflection peak. The consequence is that the colour reflected by each mixture varies under influence of the UV and it can be used as an indicator of the UV exposure itself. We present the mechanisms of the observed effects and possible application features.

This work describes the observation of lasing in an intermediate chiral phase of a dye-doped cholesteric liquid crystal mixture. This intermediate phase exists between cholesteric and smectic A phase and it presents anomalous selective reflection properties. The lasing was observed at the long-wavelength edge of the photonic band gap.

The characteristics of cholesteric liquid crystals can be controlled by light irradiation if conformationally photo-active molecules are present. Recently, control of the selective reflection band (spiral pitch) in nemato-chiral mixtures was demonstrated when photosensitive molecules, namely nematic azoxy-based compounds, were used as the host material. In this report, the investigation of light induced effects in cholesterics with azoxy-based host materials is continued to highlight the mechanisms of the response. Different non-photosensitive chiral materials were added to different azoxy-nematic liquid crystals and the pitch change caused by UV irradiation was investigated. A change in the pitch of 50–210 nm was observed depending on the exposure time and the intensity of the light. This effect is reversible: under illumination at wavelengths greater than 410 nm, the pitch shifts in the opposite direction. The dependence of the selective reflection band and the full-width-at-half-maximum of the band on the exposure time and the temperature dependence of the selective reflection band were investigated. The lowering of the phase transition temperature and narrowing of the width of the selective reflection band can be explained by a decrease in the orientational order parameter. The blue shift of the selective reflection band is due to a decrease in both the order parameter and the concentration of linear nematogenic molecules.

Sufficient slackening of degradation of the planar CLC structure and the luminescent dye in the CLC lasers was achieved rotating the CLC cell. An increase of lasing stability was demonstrated. The operating time of the laser increases by several times if compared with the fixed cells. A rotational movement of the cell was used because of its easy implementation. Degradation of the material in this case occurs along a narrow ring while the most part of the cell area remains unused. Applying more complex movements to the cell with respect to the pumping beam, allows to use the entire area of the cell and to obtain, as a result, a longer operating time of the laser. The remaining lasing instability for a moving cell is mainly expressed by the laser fluctuations which, are due to the spatial homogeneity of the CLC structure.

Trans–cis isomerization was investigated in a room temperature liquid crystal mixture of two azoxybenzene compounds. Experiments were performed on isolated molecules in dilute solutions and on the liquid crystal phase composed of the pure compounds. The absorption spectra of the trans and cis isomers were found to be similar to those of azobenzene compounds, as were the birefringence and order parameter of the nematic liquid crystal phase. The photo‐optic properties were also similar in that irradiation by ultraviolet light caused the conversion from trans to cis isomers, while short wavelength visible light incident on these compounds resulted in the conversion from cis to trans isomers. The activation energy for thermal relaxation from the cis to trans isomer in the liquid crystal phase was determined to be (66±7) kJ/mole, which is less than for azobenzene in solution. While a photostationary state in a dilute solution with approximately equal numbers of trans and cis isomers was achieved, the nematic–isotropic transition of the mixture of the pure compounds decreased from 70°C to room temperature with a cis concentration of only about 12%. One unusual finding was that the photostationary concentration of trans and cis isomers due to irradiation with light of a specific visible wavelength depended on the starting concentrations of the two isomers, indicating that there may be a molecular conformation that is not photo‐responsive and relaxes only thermally.

The lasing wavelength of dye-doped cholesteric liquid-crystal lasers is optically tuned by the reversible photoisomerization of the azo- or azoxy- nematic components of the cholesteric mixture. The figure demonstrates that the laser can be tuned over a range of almost 70 nm. The nematic components are easily and reversibly isomerized by illumination from light-emitting diodes at 405 and 466 nm.

We have investigated defect mode lasing when a cell containing a dye solution is sandwiched between two cholesteric liquid crystal cells. When the cholesteric pitch of both cells is equal, the dye emission generates the typical multi-mode lasing peaks inside the photonic stop band. We prepared two cholesteric mixtures whose pitches were shifted one respect to the other in such a way that only the edges of band gaps of the cholesteric liquid crystals layers overlapped. Using these mixtures we have observed single mode lasing. Moreover the divergence of the laser beam spot is considerably lower than the one observed in dye doped cholesteric liquid crystal lasers.

We have investigated defect mode lasing in a multilayer system consisting of a dye doped isotropic solvent sandwiched between two cholesteric liquid crystal (CLC) cells. In this case we can use dyes not soluble in liquid crystals and avoid the degradation of the CLC structure caused by the absorption of the pumping energy. When the CLC pitches of both cells are equal, the dye emission generates the typical multi-mode lasing peaks inside the photonic stop band. In CLC mixtures whose pitches were shifted one respect to the other in such a way that only the edges of band gaps of the CLC layers overlapped, we have observed single mode lasing. The divergence of the laser beam spot is considerably lower than the one observed in dye doped CLC.

Phototuning of Bragg reflection bandgap from green to blue and from red to green wavelengths was induced with a green (λ = 532 nm) laser beam in a cholesteric liquid crystal based on highly sensitive azobenzene nematic BEAM 1005 (BEAM Co.) and UV transparent non-photoisomerizable optically active dopant ZLI-6248 (R-2011) (Merck Ltd.). Optical switching between reflected and transmitted beams, as well as nonlinear transmission and reflection due to Bragg reflection band shift are studied in detail.

We present a novel design to obtain widely tunable mirror-less lasers, that combines the reflective selection properties of a broad band gap cholesteric and of a series of narrow band gap cholesterics both assembled in one system.The narrow band gap cholesterics can be obtained inducing in the same cell a variation of the helical pitch. Two strategies to vary the pitch, and then the position of the band gap are presented. The first strategy is based on the phototransformation of a photosensitive optically active dopant, while the second one relies on the variation of the concentration of a non photosensitive chiral compound. The two cholesteric layers, the one with the wide band gap material and the other one containing the narrow band gap materials, are placed at the opposite sides of a three layered cell sandwiching a mixture of isotropic solvent and a photoluminescent dye. When the pumping beam hits the cell a narrow band gap cholesteric is selected and lasing is obtained in the region where the gaps overlap. From this new device we have obtained for the first time a wider modulation of the laser emitted wavelength from 420 nm to 790 nm. With a proper dye, longer laser emission wavelengths could be achieved that would be optimal for applications in biomedicine and cosmetics.

We present the synthesis and characterization of fluorene based materials for mirror less laser applications. Mirror less lasing is obtained from a cholesteric liquid crystals mixture, that acts as a resonator, doped with a photoluminescent dye, that acts as an active medium. We propose to use fluorene based compounds to combine two necessary properties to achieve laser emission: chirality and luminescence. Two different compounds, a trimer and an oligomer are synthesized. The trimer and the oligomer are both prepared with chiral moieties and, in addition, they are liquid crystalline compatible. More, oligofluorenes are good blue emitters and the emission quantum yield is around 0.8 in the violet–blue range. These fluorene based compounds are used in cholesteric liquid crystals mixtures as luminescent chiral dopants and a fine tuning of the laser emission is obtained. The dependence of lasing efficiency on concentration and the handedness of chiral luminescent dopants are investigated.

The Erythemal Response Spectrum is a scientific expression that describes the skin sensitivity to the ultraviolet radiation. A long exposure to UV radiation causes skin erythema once a threshold dose has been exceeded.

We present a sensor based on a liquid crystalline mixture, containing dye, that absorbs photons at UV wavelength and emits them in the visible range of the electromagnetic spectrum. In particular the absorption spectrum of the mixture can be modulated to be similar to the Erythemal Response Spectrum. This system presents several innovative features: the absorption range of the mixture can be varied to be sensitive to different wavelengths, the luminescence intensity can be tuned, the system can be implemented on flexible devices, providing the possibility to create a dosimeter for ultraviolet radiation.

Lasing from dye doped cholesteric liquid crystal mixture was experimentally observed several years ago but in despite of all the efforts that have been done so far mirror less liquid crystals lasers are not yet suitable for practical applications. The main issues that have still to be addressed concern the efficiency, the stability and the tunability of the laser emission. This work has been aimed to obtain an improvement in lasing stability from dye doped chiral mixtures confined in glass cells. Stability problems are mainly related to the absorption of the powerful pumping beam from the mixture that leads to a deformation of the cholesteric texture and a bleaching of the dye. To solve these problems we have investigated different surface coatings and new system configurations.

Novel combinations of liquid crystalline materials for liquid crystals lasers tuning are presented. The cell is based on a three layer system, with two cholesteric films sandwiching a third layer containing an isotropic mixture of a photoluminescent dye. One of the cholesteric films has a wide band gap and the other one presents a narrow band gap, allowing the laser emission tuning over a wide spectral range, from UV to near IR. Further, using mixtures containing cholesteryl esters, a temperature control can be achieved.

Cholesteric liquid crystals with long pitch confined in homeotropic cells can be used to generate stable but distorted and localized liquid crystal structures exhibiting spherulitic textures, known as “bubbles.” As these bubbles can be induced by an external electric field with a narrow range following the confinement ratio C=d/p ≈1 (d representing cell thickness and p representing cholesteric pitch), it is possible to obtain electrically controlled micro-lenses. Here we investigated the optical and electro-optical properties of such liquid crystal bubbles for creating an array of micro-lenses with electrically tunable focal length.

Two ways of employing cholesteric liquid crystals in tunable dye lasers are considered: the cholesterics as distributed feedback medium and the cholesterics as resonator mirrors. In the dye doped distributed feedback cholesteric liquid crystal lasers the frequency tuning is achieved exploiting light induced effects or using a specially designed cell assembling a chiral dopant concentration gradient in combination with suitable distribution of different dyes. Another approach represents the lasing in a multilayer system consisting of a dye doped isotropic solvent sandwiched between two CLC layers. To summarize, we have demonstrated recent advances in obtain widely tunable lasing from ultraviolet wavelengths, through the visible range, to infrared wavelengths by employing cholesteric liquid crystals in dye lasers 

In this paper we propose a new method of information recording based on the photo controllable shift of the selective reflection wavelength in photo sensitive cholesteric liquid crystals. In our experiments we used a cholesteric mixture of the nematic Zhk-440 (from NIOPIK, Moscow) and optically active dopant MLC-6248 (from Merck, Germany). ZhK-440 is an azoxy-component mixture of 2/3 p-n-butyl-p-methoxyazoxybenzene and of 1/3 p-nbutyl-p-heptonoiloxyazoxybenzene. It is enough transparent in the visible range of spectrum and absorbs in the UV part. Exposure to UV shifts the selective reflection band (color) from red to green. By means of a mask covering the pattern, gratings in these structures were recorded. The gratings represent interchanging color stripes. The difference between colors depends on the exposure time.

Electrically induced and controlled gratings in large pitch cholesteric liquid crystals were investigated. Specially selected surface anchoring conditions together with well defined properties of cholesterics allow the formation of a stable periodic structure in the presence of a suitable external electric field. Polarization properties of first diffraction orders have been investigated as a function of the angle between the laser linear polarization and the grating direction. We propose to use two 1D gratings to create a 2D electrically controllable diffraction pattern, suitable for application in 3D optical devices.

Thermal and electrical tuning of laser emission from optically pumped blue phase I of dye-doped short pitch cholesteric mixtures have been achieved. Temperature changes or applied electric field to the liquid crystal cells induce structural changes in the blue phase configuration, producing a shift of the photonic band gap. The emission tunability in a structure that in addition allows multidirectional emission may herald a new age of multipurpose laser sources. Furthermore, the reversibility of the effect points out the potential applications of these soft photonic self-assembled materials.

We report on a novel technology to fabricate reflective CLC mirrors on flexible paper like substrates. The not encapsulated design and the peculiar architecture of the device significantly reduce the light scattering and provide a uniform reflection of the incident light. Depending on its thickness, the cover polymer film acts as half-wave or quarter-wave plate, which provides the desired state of polarization for the reflected light. Due to its low cost, light weight, flexibility, durability, easy technology and high reflectivity, the proposed paper based cholesteric mirror offers a novel engineering solution in applications such liquid crystals displays. As an example, they may be used as selective reflectors in guest host displays, where the guest-host system can contain a complementary colour with respect to the selective reflection of the cholesteric mirror. Additionally, the patterning of the reflector also opens up a way to make cheaper reflectors than the silver coated ones used nowadays in the display technology, with more flexibility, for any backlight or reflective display application [29]. Flexible mirrors may also find applications in optoelectronics, e-readers, smart credit cards and labels, adaptive optics, astronomy, medicine, defectoscopy, UV dosimetry.

Our assumption that micellization process in compositions containing spiropyrans of certain type would increase efficient photosensitivity was confirmed experimentally. The efficient photosensitivity of the cholesteric liquid crystal composition doped with long-radical spiropyrans to ultraviolet radiation exceeded that of the composition doped with short-radical ones. This is likely to be caused by the fact that, in the presence of the long alkyl radical at the nitrogen atom, the merocyanine form of the spiropyran molecule with a lyophilic zwitterionic head and a lyophobic nonpolar tail is amphiphilic. Under certain conditions, molecules of this kind self-organize into micelles, which disturb the thermodynamic equilibrium in the basic solution. For restoring the thermodynamic equilibrium, merocyanine molecules add to the photoinduced merocyanine ones, which eventually increases the number of absorption centers. By choosing the nematic-chiral liquid-crystal solvent possessing the properties contributing to the micellization allowed us to improve the efficient photosensitivity of long-radical spiropyrans. We observed this process in both the composition and the films obtained on their basis by microcapsulation.

Penetration of near infrared radiation (NIR) through biological tissues (human wrist, muscle and skin of hen, muscle of mollusk) was studied. The possibilities of visualizing various objects within biological tissues were examined. It is found that: (a) it is possible to see small objects with millimeter and sub-millimeter dimensions; and (b) by using NIR rays it is possible to distinguish different parts of small homogeneous biological tissues. NIR can be a possible tool in the near future to visualize millimeter size cancerous outgrowths located inside human body cavities. It will enable diagnosis of cancer at an early stage of development.

A new type of lasing was obtained on the basis of a dye-doped cholesteric liquid crystal laser with transversally distributed excitation. Two coherent beams of the pumping laser formed an interference pattern in the planar dye-doped cholesteric layer and provided laser generation in the separate narrow strips of the pumped area. Each of the strips demonstrated lasing along the cholesteric axis. But, due to the mutual coherence of the separate strips emission, the total picture of lasing represented an interference pattern. Thus, in contrast to the conventional lasers, the intensity distribution in the laser emission pattern had a periodical character similar to diffraction from an elementary dynamic hologram.

We describe a new method that enables to evaluate the temperature of the medium surrounding silver NPs as a function of the exposure time to light radiation. This method relies on the optical properties of cholesteric liquid crystals, confined into microdroplets dispersed in the medium, and combines the advantages of high spatial resolution and good temperature accuracy with fast readout. This method can be used for any NPs, disregarding their size or shape, for instance silver or gold based, and it is useful to calibrate the local temperature increase due to laser irradiated NPs in a variety of materials including particles in an inorganic or organic matrix. It is worth noting that the CLC microdroplets can be obtained in a water based environment and with a size comparable to the one of living cells. Hence, the micron size droplets act as microthermometers, providing a local visualization of the temperature reached by the medium surrounding NPs. Moreover, the proposed technique overcomes the problem to suitably cap NPs with molecules necessary to improve their miscibility in liquid crystals. The NCE used for the experiments described in this work contains a cholesteric liquid crystal with a working temperature range around 28°C-49°C, which is well suitable for applications in the biological field. Nevertheless, the cholesteric liquid crystal optical properties can be tailored to change the temperature interval to suit other applications.

Advanced countries need simple, effective and affordable novel technical solutions for anti-counterfeiting, authentication, identification and traceability of goods for security, health, justice, logistics, and industry. Nanotechnologies, in particular soft materials and biomaterials, offer new possibilities of overt and covert layers for combating fraud and related corruption. Lasing, interferential reflection, light modulation, and photonic effects can be easily combined to give an amazing amount of possible solutions.

We presented a novel cell design to obtain multicolor lasing exploiting the selective reflection properties of cholesteric materials. This result is achieved using three cholesteric liquid crystal mirrors in combination with a photoluminescent layer. The three cholesteric mirrors are prepared so that their photonic band gaps have overlapping edges. Further, applying an electric field, one of the laser lines can be switched off. This is due to the electrically induced perturbation of the local cholesteric order in one of the CLC mixtures. Other laser lines can be added simply increasing the number of layers and choosing the proper dyes and they can, eventually, be switched off by applying an electric field. Therefore, this cell is the basic element of a single compact device able to produce and control several laser beams at the same time and along the same propagation direction with possible applications for instance in biology [19], medicine [20], data recording and storage [21] or advanced microscopy

We report a method to obtain a light-controllable dichroism. The main effect is achieved using spiropyran-doped (SP-doped) nematic liquid crystal mixtures. SP molecules exhibit a high solubility in the liquid crystal host, which can vary between 1% and 4% in weight, without destroying the liquid crystalline phase. Due to their elongated shape, SP molecules are oriented along the nematic liquid crystal director. The obtained linear dichroism was measured to be 1.08 with a dichroic ratio of 7.12. Further, a two-direction linear dichroism was obtained by adding a dichroic dye to the mixture. The angle between the two dichroic axes was found to be 11°. Two-direction linear dichroism is also light controllable and can be switched back to one-direction dichroism

Surface plasmon field of metal nanoparticles, in particular of AuNPs, may be used for artificially manipulating fluorescence and, for instance, to improve biological imaging. In this paper, we used a combination of AuNPs and the fluorescence dye (FITC) for a cellular imaging of LSCM, where the skeletal muscle cells from lungfish Protopterus annectens were tested for the endothelial NOS localization. The Ar+ laser 458/488/496/514 nm was used as pump beam for the eNOS localization in sarcolemma. For each LSCM imaging, a single laser is used to irradiate the sample. The higher optical contrast between the autofluorescence and eNOS emitted signal is obtained when the AuNPs treated sample is irradiated with the laser beam at 496 nm and the emitted signal is detected in the 506-750 nm range, since this wavelength is within the SPR band of AuNPs and it is the closer one to the excitation peak of FITC (494nm). ESEM images provide more information about the AuNPs distribution in cells. The AuNPs are localized in the sarcoplasm and the vascular endothelium avoiding nuclei, which confirms the AuNPs attachment via hydrophilic forces. These AuNPs result to be ideal to skirt the overlap problem between the autofluorescence and the FITC emitted signal, since they are placed closely to FITC dyes bound to eNOS, which results to an enhancement of FITC fluorescence, providing higher optical contrast. To distinguish between eNOS localized in sarcolemma and eNOS localized in vascular endothelium, nuclei are counterstained with PI. For that, in addition to the PMT1 detecting the FITC emitted signal, the PMT2 was set to detect the PI emitted signal. Since there is an overlap between the fluorescence spectra of PI bound to nuclei and FITC-conjugated anti-rabbit polyclonal antibodies bound to eNOS, the PMTs detected ranges were set in order to minimize the maximum crosstalk between the two signals.

In this paper, FRET between GNPs (donors) and dyes (acceptors) is used for the detection of GNPs aggregation through LSCM. Moreover, DNA form Salmon tests was tested for the GNPs aggregation growth. The 514 nm was used as pump beam to irradiate the sample, since this wavelength is within the SPR of GNPs and the excitation bandwidth of the fluorescence dye (NB). Thus, the fluorescence was manipulated with the SPR through the FRET process. The fluorescence spectra and peak are, respectively, broadened and shifted, which allowed the detection of the GNPs aggregation. In the presence of DNA, the fluorescence spectrum is more redshifted due to the size increase of GNPs aggregation induced by DNA. This result is confirmed with ESEM images which also showed a GNPs assembly into denser clusters in the presence of DNA. Moreover, for a higher ESEM image magnification, GNPs are assembled in 3-D structures following the helical morphology of DNA. DNA induced GNPs aggregation growth due to the electrostatic and hydrophobic interactions between positively-charged head groups of cationic surfactants coating GNPs and negatively-charged DNA phosphate backbone. Furthermore, these results may be helpful in the world of nanobiotechnology (gene delivery, cancer therapy, etc) mainly that the DNA-binding NB molecules are not toxic [17,18] and aggregated GNPs were usually detected via light scattering techniques, which can present problems since several structures within biological tissues also scatter light strongly. Thus, FRET between GNPs and dyes detected through LSCM result to be ideal for further bio-applications to discriminate aggregated GNPs and complex structures of tissue and cells.

Rewritable optical storage has been obtained in a spiropyran doped liquid crystal polymer films. Pictures can be recorded on films upon irradiation with UV light passing through a grayscale mask and they can be rapidly erased using visible light. Films present improved photosensitivity and optical contrast, good resistance to photofatigue, and high spatial resolution. These photochromic films work as a multifunctional, dynamic photosensitive material with a real-time image recording feature.

In summary, we have demonstrated a novel, light controlled drug delivery system, based on SP doped NLC micro spheres. Experimental results have shown that upon exposure to UV/violet light, the photochromic molecules located inside the NLC spheres, experience an interconversion from the hydrophobic, oil soluble, non-polar SP state, to the hydrophilic, water soluble, highly polar MC state. Light induced photoisomerization destabilize NLC-water interface, stimulates the translocation of MC molecules across the NLC- water barrier and results their homogeneous distribution throughout in an aqueous environment. Proposed strategy can be considered as a new platform for the photostimulated drug delivery systems that offer the possibilities of the controlled delivery and release of a wide variety of drugs into the body, at the suitable time and desired site, to fight different kinds of diseases including cancer diseases.

Measuring temperatures at small scales, especially around nanoparticles, is a crucial step for a variety of applications in biomedicine and in optics. Here, we report on a novel method to map temperature in the medium surrounding silver nanoparticles dispersing them in a thermochromic mixture prepared using an organic dye and a polymer. When the nanocomposite is irradiated with visible light, nanoparticles convert light into heat and the nanocomposite changes its colour. The temperature around silver nanoparticles can be, then, easily evaluated from this colour variation. The proposed method can be implemented in temperature monitoring devices of the nanoparticles surrounding media.

In conclusion, we present a method based on laser spectroscopy to detect the presence of small amounts of acids. The system is based on the laser emission from a cuvette containing a Nile Red solution. The laser wavelength is sensitive to the chemical species and their concentration. This technique is precise and provides real time monitoring. Further, using other pH sensitive dyes, as Congo Red, more compact and cheap laser sources can be used to stimulate the laser emission from the pH sensitive mixture, as nitrogen lasers. We envisage versatile application in many fields of science and industry where the accuracy, rapidity and portability play an important role as in global and homeland security, medicine and food industry.

The visualization and control of optical to thermal energy conversion in nano and microstructures is a key challenge in many fields of science with applications to areas as nanofluidics, nanocatalysis, photothermal cancer therapy, drug delivery, imaging and spectroscopy, information storage and processing, nanoscale patterning and solar energy harvesting. In the presented work a polymer nanocomposite incorporated with silver nanoparticles and organic luminescence dye has been fabricated, which exhibits thermo chromic properties. It was shown that this kind of composite dramatically changes its color when changes an environmental temperature and acts as a thermo chromic material with such improved parameters as temperature controlled fine-tuning of absorption. This combination of silver nanoparticles and organic luminescent dyes can find versatile application in the areas such as: fabrication thermo addressable luminescence displays and thermo optical printers, environmentally friendly thermo chromic clothes. In medicine: modeling, simulation and visualization of heat spreading to the surrounding biological medium, new possibilities for measuring the heat release at the nanoscale, fabricating nano sized storage media for quantum information devices, thermo controllable filters, windows and smart coatings, infrared image converters. A simple technology promises to fabricate thermo chromic material based cost-effective devices.

Microdroplet systems have attracted great interest because of their wide range of applications, easiness in processing and handling, feasibility in developing miniaturized devices with high performances and large flexibility. In this study, a stable emulsion based on different dye-doped chiral liquid crystal droplets has been engineered in order to achieve simultaneous omnidirectional lasing at different wavelengths. To obtain the mixed emulsion of dye doped Bragg onion-type microresonators the twofold action, as a surfactant and a droplet stabilizer, of the polyvinyl alcohol dissolved in water has been exploited. Multiple wavelengths lasing in all directions around the mixed emulsion is demonstrated. By water evaporation, a plastic sheet including different types of chiral droplets is also obtained, retaining all the emission characteristic of the precursor emulsion. A relevant feature is the large flexibility of the preparation method that enables an easy and full control of the lasing spectrum addressing white laser systems. However, the simplicity of the procedure based on a single-step process as well as the high stability of the mixed emulsion is a relevant result, envisaging strong potentiality for developing easy and friendly technologies useful in the field of identification, sensing, imaging, coating and lab-on-a-chip architectures.

We have demonstrated the possibilityof grating recording in a7μm thick photosensitiveand purely optically active CLC layer, where no opticalanisotropy and selective reection are observed. There-fore, for the rst time, it is shown the possibility of gratingrecording in a few microns thick optically active layerwhere, at the same time, all the other optical properties,such as linear birefringence, absorption, reection andscattering, remain practically incidental. The process isbased on the photo-induced phase transition from the op-tically active CLC to the isotropic phase, which results inthe optical rotation angle change from 90 to 0 degrees,hence, to the change from maximum to zero optical trans-mission. Femtosecond pulses are also tested and shownto be compatible with the photo-induced changes of theoptical rotation in the CLC cell. Applications in thin grat-ings and optical information storage can be foreseen onthis basis, exploiting the unique properties of large opticalactivity of chiral liquid crystals.

In the last decade, much interest has grown around the possibility to use liquid-crystal droplets as optical microcavities and lasers. In particular, 3D laser emission from dye-doped cholesteric liquid crystals confined inside microdroplets paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small microresonators as, for example, dispersing a liquid crystal inside an immiscible isotropic fluid to create an emulsion. Recently, the possibility to obtain a thin free-standing film starting from an emulsion having a mixture of water and polyvinyl alcohol as isotropic matrix has been reported. After the water evaporation, a polymeric film in which the microdroplets are encapsulated has been obtained. Bragg-type laser emission has been recorded from the emulsion as well as from the thin film. Here, we report on the possibility to tune the laser emission as a function of temperature. Using a chiral dopant with temperature dependent solubility, the emitted laser wavelength can be tuned in a range of 40 nm by a temperature variation of 18 °C. The proposed device can have applications in the field of sensors and for the development of anti-counterfeiting labels.

In summary, for the first time is demonstrated the fabrication of a rewritable QRs, imprinted on SP doped polymer dispersed CLC films, suitable for anti-counterfeiting and security applications. By alternating UV and visible lights, images on the photochromic films can be written/erased up to 70 times, without compromising their readability. Low-cost, simple-to-fabricate, simple-to-operate and quick update feature of the films promise to produce high-quality visual QR codes that can be scanned and read out using conventional devices, such as smartphones. Furthermore, the stimuli-responsive luminescence switching properties of the proposed films may be widely acceptable to the development of novel functional materials based information storage holographic systems and devices suitable for the high-resolution spatiotemporal imaging in biological samples.

It’s known that prostate-specific membrane antigen (PSMA) is one of the most well established and highly specific prostate epithelial cell membrane antigens. PSMA is a type II transmembrane zinc metallopeptidase, belonging to the M28 peptidase family. It possesses hydrolyzing enzyme activities and is also known as FOLH1 (foliate hydrolase 1). The combination of a nanoparticle platform with targeting ligands for tumor cell-surface biomarkers is a promising architecture for achieving selective drug delivery and uptake into target cells. Gold nanoparticles (GNPs) are prone to be attached to many biological probes such as antibodies, enzymes, lectins, glycans, nucleic acids, and receptors. In this study as the prostate cancer (CaP) biomarker, we propose GNPs functionalized with PSMA and fluorescent dyes. We have investigated a possibility to obtain an increased 382fluorescence signal, gained from GNPs conjugated with fluorescent dye and PSMA. The electric charge on the GNPs, the distance between GNPs and luminescent dye molecules has a significant effect on the luminescence intensity, and this enhancement highly depends upon the excitation wavelength of pumping laser source. Charged antigen, such as PSMA, can absorb on GNPs via electrostatic interaction. As the in vitro platform, we have used a biotissue mimicking phantoms based on gelatin matrix. Gelatin-based materials are attractive due to their stable mechanical properties and ease of fabrication. Proposed method that is specific and reliable for detecting cancers at early stages and is easily accessible so that it can function as the first-line guidance is of utter importance. Further, the unique physical properties of developed nanoscale materials can be utilized to produce novel and effective sensors for cancer diagnosis, agents for tumor imaging, and therapeutics for treatment of cancer.

Using a surface force apparatus, a cholesteric liquid crystal was confined between two crossed cylindrical surfaces that induced strong planar anchoring and normal alignment of the chiral helix. The film thickness and total twist angle of the chiral molecular structure were simultaneously measured using multiple-beam optical interference. As the film thickness was increased and the chiral structure deformed, the twist angle remained almost unchanged until discontinuous changes occurred at critical distances that were equally spaced by one cholesteric half-pitch length. Structural deformations generated oscillatory elastic forces with periodically spaced maxima corresponding to twist transitions. These findings were reproduced using an equilibrium model of cholesteric confinement and force generation. The analysis indicates that the strength of the azimuthal surface anchoring on mica is high, exceeding 0.2 mJ m⁻².

In this paper, we fabricated and described a thermal imaging apparatus, which combines the attributes of weak first-order phase transitions between BPI and BPII to the brilliant colors of BPI and BPII caused by the selective reflections. The presented thermal imaging device offers several advantages over traditional thermal imaging systems. First and foremost, it does not require the cooling systems and can operate at room temperature. Furthermore, due to the high spatial resolution, small size, lighter weight, low cost, and real-time operation capabilities the proposed device can be used successfully in many different fields, ranging from medicine to the artworks inspection.

A thin layer of the photosensitive cholesteric liquid crystal possessing a high value of the optical activity is studied. Reversible change in the optical activity controlled by two light emission diodes (LEDs) with different emission wavelengths is applied for information recording. The behavior of this structure under exposure to UV and blue light is investigated. A smooth decrease in optical activity caused by the UV light resulting in a change in the color of the structure between crossed polarizers is obtained. The reverse process occurs under exposure to the blue light. On the basis of the obtained results, two methods of optical information recording in such a layer have been demonstrated.

In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60 nm. This effect could find applications for the development of spectroscopy based sensors.

In conclusion, we have demonstrated an omnidirectional lasing from dye-doped liquid crystal BPII and BPI microspheres. Due to the temperature-dependent selective reflection of BPI, the temperature-controlled lasing tuning of about 55 nm was obtained. The temperature guided broad tuning range of BP lasers, coupled with their self-assembly behavior and microscopic sizes provides a number of applications of these materials in areas such as sensing, smart optical filters, diagnostics, thermo-addressable optical filters, displays and optical lenses

We have prepared the liquid crystal blue phase (BP) microdroplets emulsified in the glycerol environment and investigated their electro-optical properties upon the applied electric field. We showed that the lasing from the supercooled luminescent dye-doped BPI microdroplets can be controlled electrically. When the electric field intensity is increased, the lasing intensity is increased too along with the linewidth that decreases from 6 to 2.5 nm. Besides, the laser lines were shifted toward the shorter wavelength by 11 nm. All effects were achieved via electric field-stimulated structural and symmetrical modification of BPI microdroplets, resulting in their optical anisotropy and birefringence. Luminescent dye-doped liquid crystal blue phase-based microdroplets can find applications as electrically controlled microlaser sources for microphotonics and environmental sensing.

We prepared and investigated Nb, CaM and GNPs based nanomaterials and demonstrated that CaM conjugated with the Nb fluorescent dye and GNPs can increase its fluorescence intensity upon the excitation of a pumping laser source. The obtained results can be put forward as a useful modality for the in-vitro representation of nanoparticle-mediated cancer biomarkers, cell labelling and tracking in biological tissues through fluorescence. It opens new possibilities for plasmonic applications in nanobiology and nanomedicine.

A vast amount of nanoparticles has been developed and proposed for the local hyperthermia of cancer during the last decades, but only a few of them correspond to the mandatory requirements of

having therapeutic range Curie temperature (TC=41-450 C), high-rate crystallinity and “strong” magnetic properties, strictly controlled homogeneity and dispersion of the nanoparticles, good

biocompatibility and harmless decomposition products. Among them are the nickel-copper (Ni-Cu) and silver doped lanthanum manganite (AgxLa1-xMnO3) nanoparticles. The developed research

showed that the materials obtained at lower than usual temperatures using microwave enhanced synthesizes and annealing can be successfully used for local hyperthermia revealing high magnetic

properties. Behavioral toxicity testing of the developed nanoparticles was enhanced by blood oxygen saturation measurements using noninvasive oximetry in white rats. Both of the developed

nanomaterials revealed a lower toxicity level than the commercially available Fe2O3 nanoparticles

Hexagonal boron nitride nanoparticles, nanosheets and nanotubes (BNNPs) are even more promising materials for biomedical application than carbon nanotubes (CNTs) and nanoparticles (CNPs) due

to their negligible cytotoxicity. The reported research yielded in development and testing of two distinctive microwaves enhanced comparatively low-temperature methods of synthesis of the

hexagonal boron nitride nanoparticles and nanosheets with reduced distortion of the crystal lattice, and an improved method of general toxicity testing of the developed nanomaterials utilizing

continuous observation of behavioral effects in white rats in combination with blood oxygen saturation, systolic blood pressure and body temperature measurements in full agreement with the

4R principles of animal welfare in scientific research. The obtained results allow us to expect that the developed materials can be a good basis for developing highly effective modalities for anticancer (in

combination with chemotherapy, hyperthermia and radiotherapy) and antiviral (in combination with chemotherapy and hyperthermia) treatment.

The development of a smart microencapsulation system programmed to actively respond to environmental stimuli is gaining increasing importance compared to the traditional forms of drug administration. In this study, we introduce two new concepts of the drug delivery system, based on the light and pH-sensitive liquid crystal (LC) microspheres. The proposed system represents an emulsion formed by the immiscibility between the LC micro-spheres and a water environment.

We prepared and investigated quercetin-modified Fe3O4 nanoparticles and demonstrated that the functionalization through the conjugation of fluorescent species and magnetic nanoparticles dramatically alters the nanocomposite optical parameters such as fluorescence intensity, spectral position and shape of fluorescence emission. The proposed image-guided drug-delivery system emerges as a promising tool for in-vivo tracking of fluorescent dye-labelled therapeutic drugs with functionalized Fe3O4 nanoparticles in a complicated and delicate biological environment, such as cancer cells and BBB.

The aim of the work was to determine the possibility of assessing the state of human health by the method of optical spectroscopy of skin and nail. To achieve this goal, Laser-Induced Fluorescence (LIF) spectroscopy was used. A special probe was designed, which makes it possible to record differential spectra and, as a result, to compare the shapes of spectral fluorescence lines. In vivo spectra of LIF intensities of the human finger pad and nail were measured. These spectra can be used to determine and characterize the state of human health, and it’s also further monitoring in real time.When processing the spectra of different volunteers, it was found that the fluorescence spectra of the skin of physiologically healthy and pathological (in this case, type 1 and 2 diabetes) volunteers significantly differed from each other. Moreover, the analysis of these spectra makes it possible to assess the degree of pathology. It was also found that any of the three experimentally recorded fluorescence spectra is a superposition of the other two. A theoretical analysis of the multilayer model of human skin fluorescence has shown that this principle is always valid when the same chromophores are involved in fluorescence.

We have developed a cholesteric liquid crystal (CLC) mirror-based innovative model for detection and visualization of images in turbid media. Due to its unique optical-polarization properties, the CLC mirror is suggested as the basic element of the imaging Stokes polarimeter. The particular design of the proposed polarimeter, coupled with its distinguished operational simplicity, reliability, and real-time operational facilities, promises to fabricate a new generation of the imaging Stokes polarimeter, which can find applications in areas such as diagnostics, biology, astronomy, and remote sensing

Ultraviolet (UV) radiation is a form of electromagnetic radiation that comes from the sun and man-made sources. UV radiation can damage the DNA (genes) in cells, which in turn may lead to cancer. Most skin cancers are a result of exposure to UV rays in sunlight. We have developed a novel UV radiation dosimeter that allows a real-time estimation of the dose of harmful ultraviolet UV-A and UV-B radiations emitted by the sun and artificial sources. When exposed to UV radiation, our UV Dosimeter visibly change color from the starting yellow to blue to dark violet. The color change correlates to levels of accumulated UV radiation.