Solvatochromic behavior on the absorption and fluorescence spectra of Rose Bengal dye in various solvents

Photophysical properties of Radachlorin photosensitizer in solutions of different pH, viscosity and polarity

We present a thorough experimental investigation of fluorescence properties of Radachlorin photosensitizer in solutions of different acidity, viscosity and polarity. Experiments were performed using time-resolved fluorescence lifetime imaging and time-resolved analysis of polarized fluorescence. Variations of solution acidity resulted in considerable changes of Radachlorin fluorescence quantum yield and lifetime in the pH range from 4 to 7, but did not affect the rotational diffusion time, and almost did not change the quantum yield and characteristic times of singlet oxygen phosphorescence. Variations of solution polarity and viscosity were achieved by changing ethanol or methanol fraction in aqueous solution. The decrease of solution polarity resulted in nonlinear rise of Radachlorin fluorescence quantum yield and lifetime up to alcohol concentration of 50%-65%, as well as in considerable rise of singlet oxygen quantum yield and significant changes in characteristic times of its phosphorescence. Variations of solution viscosity resulted in changes of rotational diffusion time of Radachlorin molecules, which appeared to be in perfect correlation with methanol solution viscosity. Good correspondence with ethanol solution viscosity was observed only up to 50% alcohol fraction. Deviations of rotational diffusion time of Radachlorin molecules from direct proportionality with solution viscosity at higher ethanol concentrations were suggested to be due to different solvation conditions. The data obtained can give important reference points for analysis of microenvironment of Radachlorin molecules, their intracellular localization and performance in singlet oxygen generation.

Photodynamic therapy for the treatment of Pseudomonas aeruginosa infections: A scoping review

BACKGROUND

Pseudomonas aeruginosa is a Gram-negative bacillus that causes superficial and deep infections, which can be minor to life-threatening. Recently, P. aeruginosa has gained significant relevance due to the increased incidence of multidrug-resistant (MDR) strains that complicate antibiotic treatment. Due to MDR strains, alternative therapies, such as antimicrobial photodynamic therapy (PDT), are presented as a good option to treat nonsystemic infections. PDT combines a photosensitizer agent (PS), light, and oxygen to generate free radicals that destroy bacterial structures such as the envelope, matrix, and genetic material. This work aimed to identify the development stage of the PDT applied to P. aeruginosa to conclude which research stage should be emphasized more.

METHODS

Systematic bibliographic search in various public databases was performed. Related articles were identified using keywords, and relevant ones were selected using inclusion and exclusion criteria according to the PRISMA protocol.

RESULTS

We found 29 articles that meet the criteria, constituting a good body of evidence associated with using PDT against P. aeruginosa in vitro and less developed for in vivo research.

CONCLUSIONS

We conclude that PDT could become an effective adjunct to antimicrobial therapy against P. aeruginosa. This effectiveness depends on the PS used and the location of the infection. Many PS already demonstrated efficacy in PDT, but the evidence is supported significantly by in vitro and very few in vivo studies. Therefore, we conclude that further research efforts should focus on demonstrating the safety and efficacy of these PSs in vivo in animal infection models.

Guanine Quantum Defects in Carbon Nanotubes for Biosensing

Fluorescent single-wall carbon nanotubes (SWCNTs) are used as nanoscale biosensors in diverse applications. Selectivity is built in by noncovalent functionalization with polymers such as DNA. Recently, covalent functionalization was demonstrated by conjugating guanine bases of adsorbed DNA to the SWCNT surface as guanine quantum defects (g-defects). Here, we create g-defects in (GT)₁₀-coated SWCNTs (G^d-SWCNTs) and explore how this affects molecular sensing. We vary the defect densities, which shifts the E₁₁ fluorescence emission by 55 nm to a λ_max of 1049 nm. Furthermore, the Stokes shift between absorption and emission maximum linearly increases with defect density by up to 27 nm. G^d-SWCNTs represent sensitive sensors and increase their fluorescence by >70% in response to the important neurotransmitter dopamine and decrease it by 93% in response to riboflavin. Additionally, the extent of cellular uptake of G^d-SWCNTs decreases. These results show how physiochemical properties change with g-defects and that G^d-SWCNTs constitute a versatile optical biosensor platform.

Fluorescence-Coupled Techniques for Determining Rose Bengal in Dermatological Formulations and Their Application to Ex Vivo Skin Deposition Studies

Rose Bengal (RB) is a fluorescent dye with several potential biomedical applications, particularly in dermatology. Due to RB's poor physicochemical properties, several advanced delivery systems have been developed as a potential tool to promote its permeation across the skin. Nevertheless, no validated quantitative method to analyse RB within the skin is described in the literature. Considering RB exhibits a conjugated ring system, the current investigation proposes fluorescence-based techniques beneficial for qualitatively and quantitatively determining RB delivered to the skin. Notably, the development and validation of a fluorescence-coupled HPLC method to quantify RB within the skin matrix are herein described for the first time. The method was validated based on the ICH, FDA and EMA guidelines, and the validated parameters included specificity, linearity, LOD, LLOQ, accuracy and precision, and carry-over and dilution integrity. Finally, the method was applied to evaluate RB's ex vivo permeation and deposition profiles when loaded into dermatological formulations. Concerning qualitative determination, multiphoton microscopy was used to track the RB distribution within the skin strata, and fluorescence emission spectra were investigated to evaluate RB's behaviour when interacting with different environments. The analytical method proved specific, precise, accurate and sensitive to analyse RB in the skin. In addition, qualitative side-analytical techniques were revealed to play an essential role in evaluating the performance of RB's dermatological formulation.

Effectiveness of curcumin-based antimicrobial photodynamic therapy against Staphylococcus aureus

PURPOSE

This study investigated the effectiveness of curcumin-based antimicrobial photodynamic therapy (aPDT) against Staphylococcus aureus (S. aureus), the causative agent of ventilator-associated pneumonia.

METHODS

Curcumin was added to S. aureus culture medium at concentrations of 25, 2.5, and 0.25 µM. After 60 min (20-25°C), each culture was irradiated for 1 and 3 min, and viable bacteria were counted. Curcumin (25 µM) was also added to a bacterial suspension with D-mannitol and sodium azide; microbial counts were determined after irradiation for 3 min.

RESULTS

S. aureus was significantly reduced in the 1-min (P = 0.043) and 3-min (P = 0.011) irradiation groups in comparison to the 0-min irradiation group with 25 µM curcumin. No significant differences were observed between the curcumin alone group and the curcumin plus D-mannitol or sodium azide group.

CONCLUSION

The findings of this study indicate that prolonged exposure (≥1 min) of S. aureus to LED in 25 μM curcumin solution induces cell wall injury. Curcumin-based aPDT as an adjunct to conventional oral care, employing existing dentistry equipment, offers a promising approach that does not rely on antimicrobial drugs or allows the emergence of resistant bacterial strains. This suggests its potential role in future strategies aimed at preventing ventilator-associated pneumonia.

Investigation of bactericidal effect of a mid-infrared free electron laser on Escherichia coli

The rapid increase in the number of bacteria that are resistant to many commonly used antimicrobial agents and their global spread have become a major problem worldwide. In particular, for periodontal disease, which is a localized infection, there is a growing need for treatment methods that do not primarily involve antimicrobial agents, and antimicrobial photodynamic therapy (aPDT) is attracting attention. In this study, the bactericidal effects of a mid-infrared free electron laser (MIR-FEL) on E. coli were investigated as a basic study to examine the applicability of MIR-FELs, which can selectively excite molecular vibrations due to their wavelength tunability, to aPDT. The optimal irradiation wavelengths to be examined in this study were determined from the infrared spectrum of the bacteria, which was obtained using Fourier transform infrared spectroscopy. Five irradiation wavelengths (6.62, 6.88, 7.14, 8.09 and 9.26 µm) were selected from the FT-IR spectrum, and we found that the bactericidal effects at a wavelength of 6.62 µm were markedly stronger than those observed at the other wavelengths. At this wavelength corresponding to the Amide II band, the bacterial survival rate decreased significantly as the irradiation time increased. On the contrary, irradiation of a neodymium-doped yttrium aluminum garnet (Nd: YAG) laser at 1.06 µm exhibited no distinct bactericidal effect. No morphological changes were observed after MIR-FEL irradiation, suggesting that a bacterial organelle molecule may be the target of MIR-FEL irradiation, but the exact target was not identified. Furthermore, the temperature change induced in the culture medium by the laser irradiation was ± 1.5 °C at room temperature. These results suggest that the bactericidal effects of MIR-FEL are derived from photochemical reactions involving infrared photons, since E. coli is usually killed by heating it to 75 °C for 1 min or longer.

Ultrasmall organosilica nanoparticles with strong solid-state fluorescence for multifunctional applications

INTRODUCTION

Organosilica nanoparticles (ONs), which are a new type of photoluminescent nanomaterial (PM) with excellent biocompatibility, have caught more attention in recent years. However, their applications are significantly impeded by the complicated preparation process, poor photostability, and especially aggregation-induced quenching.

OBJECTIVES

The present study was aimed to design and prepare solid-state fluorescent ONs to avoid aggregation-induced quenching effect. In addition, the uses of ONs for fingerprint detection, white light-emitting diodes (WLEDs) and lysosome-targetable cellular imaging were demonstrated.

METHODS

Here, for the first time, we designed and prepared novel solid-state fluorescent ultrasmall ONs with orange-emitting photoluminescence via a one-step hydrothermal method.

RESULTS

The prepared solid-state fluorescent ONs could be successfully employed in fingerprint detection, WLEDs fabrication and cellular imaging. Intriguingly, the ultrasmall ONs specifically localized to lysosomes rather than other subcellular organelles across distinct cell lines, including cancer cells and noncancerous cells.

CONCLUSION

Collectively, these data showed that the new ONs presented in this study could be ideal candidates for PMs in biological and photoelectric applications.

Nanocomposites of Copper Trimesinate and Graphene Oxide as Sorbents for the Solid-Phase Extraction of Organic Dyes

A nanocomposite based on graphene oxide and copper trimesinate was obtained by the in situ method. The samples have permanent porosity and a microporous structure with a large surface area corresponding to the adsorption type I. A study of the adsorption properties of the obtained composites with respect to organic dyes (malachite green, indigo carmine, brilliant green, Rose Bengal, crystal violet) showed that adsorption largely depends on the content of graphene oxide in the composites. The complex is an effective sorbent for the extraction of cationic and neutral organic dyes when the content of graphene oxide in the nanocomposite is 20% of the calculated copper trimesinate due to electrostatic forces of interaction. For anionic dyes, the maximum adsorption is achieved when using a composite containing 5% graphene oxide due to the predominance of physical sorption. Experimental results show that the obtained sorbent can be used for extraction in a wide pH range, illustrating the excellent pH window offered by this adsorbent. Kinetics data were properly fitted with the pseudo-second-order model. Equilibrium data were best correlated with the Freundlich model. The process was endothermic and spontaneous in nature. The composite makes it possible to achieve a maximum sorption of 393 mg/g, which is a sufficiently high value for the absorption of dyes.

Photosensitized Electrospun Nanofibrous Filters for Capturing and Killing Airborne Coronaviruses under Visible Light Irradiation

To address the challenge of the airborne transmission of SARS-CoV-2, photosensitized electrospun nanofibrous membranes were fabricated to effectively capture and inactivate coronavirus aerosols. With an ultrafine fiber diameter (∼200 nm) and a small pore size (∼1.5 μm), optimized membranes caught 99.2% of the aerosols of the murine hepatitis virus A59 (MHV-A59), a coronavirus surrogate for SARS-CoV-2. In addition, rose bengal was used as the photosensitizer for membranes because of its excellent reactivity in generating virucidal singlet oxygen, and the membranes rapidly inactivated 97.1% of MHV-A59 in virus-laden droplets only after 15 min irradiation of simulated reading light. Singlet oxygen damaged the virus genome and impaired virus binding to host cells, which elucidated the mechanism of disinfection at a molecular level. Membrane robustness was also evaluated, and in general, the performance of virus filtration and disinfection was maintained in artificial saliva and for long-term use. Only sunlight exposure photobleached membranes, reduced singlet oxygen production, and compromised the performance of virus disinfection. In summary, photosensitized electrospun nanofibrous membranes have been developed to capture and kill airborne environmental pathogens under ambient conditions, and they hold promise for broad applications as personal protective equipment and indoor air filters.

"On-Demand" Antimicrobial Photodynamic Activity through Supramolecular Photosensitizers Built with Rose Bengal and (p-Vinylbenzyl)triethylammomium Polycation Derivatives

The antimicrobial photodynamic activity (aPDA) in fungal and bacterial strains of supramolecular adducts formed between the anionic photosensitizer (PS) Rose Bengal (RB^2-) and aromatic polycations derived from (p-vinylbenzyl)triethylammonium chloride was evaluated. Stable supramolecular adducts with dissociation constants K_d ≈ 5 μM showed photosensitizing properties suitable for generating singlet oxygen (Φ_Δ = 0.5 ± 0.1) with the added advantage of improving the photostability of the xanthenic dye. However, the aPDA of both free and supramolecular RB^2- was highly dependent on the type of microorganism treated, indicating the importance of specific interactions between the different cell wall structures of the microbe and the PSs. Indeed, in the case of Gram-positive Staphylococcus aureus, the aPDA of molecular and supramolecular PSs was highly effective. Instead, in the case of Gram-negative Escherichia coli, only the RB^2-:polycation adducts showed aPDA, while RB^2- alone was inefficient, but in the case of Candida tropicalis, the opposite behavior was observed. Therefore, the present results indicate the potential of supramolecular chemistry to obtain aPDA à la carte depending on the target microbe and the PS properties.

(Rose Bengal)/(Eosin Yellow)-Gold-Polypyrrole Hybrids: A Design for Dual Photo-Active Nano-System with Ultra-High Loading Capacity

Purpose

Enhancement of the photodynamic/photothermal efficiency of two water-soluble dyes, rose bengal (RB) and eosin yellow (EY), via conjugation to a polymeric nano-system gold-polypyrrole nanoparticle (AuPpy NPs).

Methodology

A multi-step synthesis method and an in situ one-pot synthesis method were used. Loading percentage, particle size, zeta potential, morphology, UV-Vis-NIR spectrophotometry and in vitro photothermal activity were measured. Then, both hybrid nanocomposites were examined for their cytotoxicity and photocytotoxicity on HepG2 cell line as a model for cancer cells.

Results

Dyes loaded in the traditional multi-step method did not exceed 9% w/w, while in the one-pot synthesis method they reached ~67% w/w and ~75% w/w for EY-AuPpy NPs and RB-AuPpy NPs, respectively. UV-Vis-NIR spectrophotometry showed that both nano-systems exhibited intense absorption in the NIR region. The mean size of the nanoparticles was ~31.5 nm (RB-AuPpy NPs) and ~33.6 nm (EY-AuPpy NPs) with zeta potential values of −26.5 mV and −33 mV, respectively. TEM imaging revealed the morphology of both hybrids, showing ultra-nano spherical-shaped gold cores in the case of RB-AuPpy NPs, and different shapes of larger gold cores in the case of EY-AuPpy NPs, both embedded in the polymer film. Conjugation to AuPpy was found to significantly reduce the dark cytotoxicity of both RB and EY, preserving the photocytotoxicity of EY and enhancing the photocytotoxicity of RB.

Conclusion

Gold-polypyrrole nanoparticles represent an effective delivery system to improve the photodynamic and photothermal properties of RB and EY. The in situ one-pot synthesis method provided a means to greatly increase the loading capacity of AuPpy NPs. While both hybrid nanocomposites exhibited greatly diminished dark cytotoxicity, RB-AuPpy NPs showed significantly enhanced photocytotoxicity compared to the free dyes. This pattern enables the safe use of both dyes in high concentrations with sustained action, reducing dose frequency and side effects.

Impact on Porphyromonas gingivalis of antimicrobial photodynamic therapy with blue light and Rose Bengal in plaque-disclosing solution

OBJECTIVES

Antimicrobial photodynamic therapy (aPDT) in periodontal pockets using lasers is difficult to perform in some cases because of the high cost of irradiation equipment and the narrow irradiation field. The purpose of the present study was to examine the effects of aPDT in combination with a plaque-disclosing solution and blue light-emitting diode (LED), which are used for composite resin polymerization.

METHODS

The reactive oxygen species generated by irradiating 0.001% RB or MB with blue light were analyzed using electron spin resonance spectroscopy. Blue-light exposure was performed at 6.92, 20.76 and 124.6 J. The microorganism to be sterilized was Porphyromonas gingivalis. After aPDT, colony-forming units (CFUs) were measured to estimate cell survival. Carbonylated protein (PC) levels were used to evaluate oxidative stress. All statistical analyses were performed with Tukey's multiple comparisons test or the unpaired t-test.

RESULTS

Singlet oxygen (¹O₂) generation was confirmed by RB+blue LED. ¹O₂ production was significantly greater with the blue LED irradiation of RB than that of MB (p < 0.0001). CFUs were significantly lower in the blue LED-irradiated group than in the non-LED-irradiated group (p < 0.01). The bactericidal effect increased in a time-dependent manner. aPDT increased PC levels. No morphological changes were observed in P. gingivalis.

CONCLUSIONS

The present results suggest that aPDT exerts bactericidal effects against P. gingivalis by increasing oxidative stress through the generation of ¹O₂ in cells. Periodontal disease may be treated by aPDT using the equipment available in dental offices.

Solvent-Dependent Spectral Properties in Diverse Solvents, Light Harvesting and Antiviral Properties of Mono-Azo Dye (Direct Yellow-27): A Combined Experimental and Theoretical Study

In this paper, we have discussed for the first time a detailed electronic absorption study of the mono-azo dye Direct Yellow 27 [C[Formula: see text]H[Formula: see text]N4Na2O9S3] (DY-27) with five different homogeneous media by applying experimental and theoretical techniques along with some new characteristics of DY-27 in the field of solar cells as well as antiviral activities. A clear absorption band in the UV-visible region was observed, although the absorption maxima lie in the visible region. The electronic absorption transitions observed in our study were fully spin and symmetry allowed transitions with [Formula: see text]–[Formula: see text] character. Time-dependent density functional theory (TD-DFT) analysis has been done for understanding the electronic and the charge transfer performance. Moreover, the impacts of polar protic and polar aprotic solvents in the structural variation of DY-27 have been reported here. Further, applications of the dye in the field of solar cell, as well as antiviral activity, were performed using molecular modeling approaches. The dye exhibited a D–[Formula: see text]–A–A structure with a high light-harvesting efficiency (LHE) and good injection efficiency acts as an effective dye sensitized solar cell (DSSC). Molecular docking studies of the dye DY-27 performed with M-protease of the different corona viruses, MERS, SARS-CoV-1 and SARS-CoV-2 indicated comparable binding energies with the controlled inhibitors and best interactions are observed for the SARS-CoV-1.

Impact of binding to the multidrug resistance regulator protein LmrR on the photo-physics and -chemistry of photosensitizers

Light activated photosensitizers generate reactive oxygen species (ROS) that interfere with cellular components and can induce cell death, e.g., in photodynamic therapy (PDT). The effect of cellular components and especially proteins on the photochemistry and photophysics of the sensitizers is a key aspect in drug design and the correlating cellular response with the generation of specific ROS species. Here, we show the complex range of effects of binding of photosensitizer to a multidrug resistance protein, produced by bacteria, on the formers reactivity. We show that recruitment of drug like molecules by LmrR (Lactococcal multidrug resistance Regulator) modifies their photophysical properties and their capacity to induce oxidative stress especially in 1O2 generation, including rose bengal (RB), protoporphyrin IX (PpIX), bodipy, eosin Y (EY), riboflavin (RBF), and rhodamine 6G (Rh6G). The range of neutral and charged dyes with different exited redox potentials, are broadly representative of the dyes used in PDT.

Extraction, optical properties, and aging studies of natural pigments of various flower plants

In this paper, we reported the extraction process of five different flowering plants utilizing different dye extraction methods and solvents (ethanol and water) to choose the best dye removal process. The FTIR spectra revealed the presence of several clear functional groups for all five natural dyes. The analytical studies such as UV spectroscopy, column chromatography, and vacuum evaporation were performed to isolate the dyes from their solutions. The UV-Vis studies on the pigments of flower extracts indicated broad absorption peaks in the visible region including clear bandgaps. Among the studied pigments, Alternanthera ficoidea showed the lowest direct bandgap of 1.69 eV and an Urbach energy value of 6.33 meV. The dye extraction yield rate improvement was extended from 11.7 to 24.7% (water solvent) and 11.3-32.4% (ethanol solvent). Throughout the studies, it was observed that ethanol produced a better extraction for organic dyes than water as a solvent. Aging studies revealed that all the dyes at the room temperature showed better stability with minor changes in the observed optical parameters in oxygen-rich conditions; however, these parameters have shown significant variations at a 60 °C temperature.

Dark Antibacterial Activity of Rose Bengal

The global spread of bacterial resistance to antibiotics promotes a search for alternative approaches to eradication of pathogenic bacteria. One alternative is using photosensitizers for inhibition of Gram-positive and Gram-negative bacteria under illumination. Due to low penetration of visible light into tissues, applications of photosensitizers are currently limited to treatment of superficial local infections. Excitation of photosensitizers in the dark can be applied to overcome this problem. In the present work, dark antibacterial activity of the photosensitizer Rose Bengal alone and in combination with antibiotics was studied. The minimum inhibitory concentrations (MIC) value of Rose Bengal against S. aureus dropped in the presence of sub-MIC concentrations of ciprofloxacin, levofloxacin, methicillin, and gentamicin. Free Rose Bengal at sub-MIC concentrations can be excited in the dark by ultrasound at 38 kHz. Rose Bengal immobilized onto silicon showed good antibacterial activity in the dark under ultrasonic activation, probably because of Rose Bengal leaching from the polymer during the treatment. Exposure of bacteria to Rose Bengal in the dark under irradiation by electromagnetic radio frequency waves in the 9 to 12 GHz range caused a decrease in the bacterial concentration, presumably due to resonant absorption of electromagnetic energy, its transformation into heat and subsequent excitation of Rose Bengal.

Effect of hybrid SiO2@Ag nanoparticles with raspberry-like morphology on the excited states of the photosensitizers Rose Bengal and riboflavin

Ag⁺ is released due to a charge transfer process from the triplet state of adsorbed riboflavin to the silver nanoparticles.

Synthesis and photophysical properties of deuteration of pirfenidone

In order to improve the metabolism of pirfenidone (5-methyl-1-phenylpyridin-2-one, PFD), the methyl-deuterated version of pirfenidone via the substitution of hydrogen (H) at C-5 by its isotope deuterium (D, 5D-PFD) was synthesized and its photophysical properties were investigated. The negative solvatochrom was observed in absorption and fluorescence spectra with increasing solvent polarity, which implied that intermolecular charge transfer (ICT) involved n → π* transition for both of PFD and 5D-PFD. The ground state and excited state dipole moment was calculated as 5.30 D and 3.30 D for PFD, and 3.70 D and 2.18 D for 5D-PFD, respectively, which suggested the more polar nature of PFD in the ground state than that of excited state compared with 5D-PFD. Density functional theory (DFT) results demonstrated a significant propensity of ICT from the electron-donor, methyl and carbonyl group to the amine group as an electron donor. The binding of metal ions with PFD or 5D-PFD induced a red-shift of π → π* transition and blue-shift of n → π* transition, respectively, indicating that the pyridone ring showed more stability upon binding of unoccupied orbital of metal ions with lone-pair electron of oxygen atom and thus prompted the electronic distribution on phenyl unit. Upon addition of metal ions, the aromatic region presented the characteristic upfield shifts, and the resonance contributed by 3-H showed a significant downfield chemical shift/deshielding effect, indicating the deduced resonance of 3-H and the improved electron distribution of phenyl unit. The binding and docking of human serum albumin showed that the affinity of 5D-PFD with HSA was lower than that of PFD, and also 5D-PFD might prefer to present free forms in the blood with better efficacy comparing with PFD. The pharmacokinetic of half-time (T_1/2) for oral and i.v. administration of 5D-PFD was found around 19 and 30 min, higher than that of i.v. administration of PFD, 8.6 min, reported by Giri et al. The results of this work suggest that the deuteration enhances the metabolism of PFD significantly with little change of physical-chemical property.

Cytotoxicity of multifunctional surfactant containing capped mesoporous silica nanoparticles

This paper reports the synthesis of silica capped surfactant (CTAB) and dye (Rose Bengal; RB) containing mesoporous silica nanoparticles (MSNs).

Photochemistry of rose bengal in water and acetonitrile: a comprehensive kinetic analysis

A comprehensive investigation of the photophysical properties and the photochemistry of rose bengal provided detailed information about the kinetics and the optical properties of all major intermediates involved.

Preparation and characterization of uniform near IR polystyrene nanoparticles

Biomaterials for in vivo fluorescence imaging are required to be biocompatible, nontoxic, photostable and highly fluorescent. Fluorescence must be in the near infrared (NIR) region of the electromagnetic spectrum to avoid absorption and autofluorescence of endogenous tissues. NIR fluorescent polystyrene nanoparticles may be considered ideal biomaterials for in vivo imaging applications. These NIR nanoparticles were prepared by a swelling process of polystyrene template nanoparticles with a hydrophobic NIR dye dissolved in a water-miscible swelling solvent, a method developed for preparation of nonbiodegradable nanoparticles, for NIR fluorescent bioimaging applications. This method overcomes common problems that occur with dye entrapment during nanoparticle formation such as loss of fluorescence and size polydispersity. Fluorescence intensity of the nanoparticles was found to be size dependent, and was optimized for differently sized nanoparticles. The resulting NIR nanoparticles were also found to be more fluorescent and highly photostable compared to the free dye in solution, showing their potential as biomaterials for in vivo fluorescence imaging.

Hydrophilic gel composition effect on the molecular association and spectroscopic behavior of rhodamine B

Electronic absorption spectra of rhodamine B dye in aqueous solutions and in a polyacrylamide hydrogel matrix with different structural compositions were studied at room temperature. The transport and the solute–solute interactions of rhodamine B in aqueous solutions across the hydrophilic gels were investigated via exploration of the spectral properties of the dye-loaded hydrogel. The nature of the dye pair interactions in these media was discussed using the Kasha exciton theory. In addition, the monomer–dimer equilibrium of rhodamine B molecules in hydrogels with different compositional percentages was studied by means of UV–vis spectroscopy and least-squares fitting methods.

Solvent effect on the absorption and fluorescence of ergone: determination of ground and excited state dipole moments

The effect of solvents on the absorption and emission spectra of ergone has been studied in various solvents at 298 K. The bathochromic shift was observed in absorption and fluorescence spectra with the increase of solvents polarity, which implied that transition involved was π→π*. And the normalized transition energy value E(T)(N) showed some scattering when plotted versus Δν. The ground state and excited state dipole moments were calculated by quantum-mechanical second-order perturbation method as a function of the dielectric constant (ε) and refractive index (n). The result was found to be 1.435 D and 2.520 D in ground state and excited state respectively. And also, the density functional calculations were used to obtain the ground state and excited state dipole moments for it has proven to be suitable for calculating electronic excitation energy. And the result is consistent with the experimental.