Ripon Sarkar

ROS generation by reduced graphene oxide (rGO) induced by visible light showing antibacterial activity: comparison with graphene oxide (GO)

Reduced graphene oxide (rGO) generates reactive oxygen species (ROS) under visible light in air via a singlet oxygen–superoxide anion radical pathway which readily kills Enterobacter sp. The rGO+ intermediate reacts with a hydroxyl ion to produce graphene oxide (GO) as a coating on the surface of rGO resulting in enhanced fluorescence and a slow down in photo-induced ROS formation. GO is not toxic but on ageing it gets a surface coating of rGO and shows toxicity.

Simple Bisthiocarbonohydrazone as a Sensitive, Selective, Colorimetric, and Ratiometric Fluorescent Chemosensor for Picric Acids

A bisthiocarbonohydrazone-based chemosensor molecule (R1) containing a tetrahydro-8-hydroxyquinolizine-9-carboxaldehyde moiety has been synthesized and characterized as a new ratiometric fluorescent probe for picric acid (PA). The ratiometric probe R1 is a highly selective and sensitive colorimetric chemosensor for PA. The association between the chemosensor and PA and the ratiometric performance enabled by the key role of excited state intramolecular proton transfer in the detection process are demonstrated. Selectivity experiments proved that R1 has excellent selectivity to PA over other nitroaromatic chemicals. Importantly, the ratiometric probe exhibited a noteworthy change in both colorimetric and emission color, and this key feature enables R1 to be employed for detection of PA by simple visual inspection in silica-gel-coated thin-layer chromatography plates. Probe R1 has been shown to detect PA up to 3.2 nM at pH 7.4. Microstructural features of R1 and its PA complex have been measured by a field emission scanning electron microscope, and it clearly proves that their morphological features differ dramatically both in shape and size. Density function theory and time-dependent density function theory calculations were performed to establish the sensing mechanism and the electronic properties of probe R1. Furthermore, we have demonstrated the utility of probe R1 for the detection of PA in live Vero cells for ratiometric fluorescence imaging.

A Michael addition–cyclization-based switch-on fluorescent chemodosimeter for cysteine and its application in live cell imaging

Based on a conjugate addition/intramolecular cyclization sequence, we designed and synthesized a fast response fluorescent probe, BTAC (benzothiazol-azacoumarin), for the discriminative detection of cysteine (Cys). The reaction of cysteine with BTAC results in the cleavage of the acrylate moiety from BTAC, thereby producing BTAC-OH, with a remarkable fluorescence enhancement at 560 nm. The probe exhibits high sensitivity and selectivity toward cysteine over homocysteine and glutathione and the detection limit reached as low as 124 nM for cysteine. The addition of Cys resulted in the color of the solution of BTAC changing from colorless to greenish yellow under the simulation of physiological conditions and BTAC could serve as a “naked-eye” indicator. The structure of BTAC was established by computational DFT (density functional theory) calculation and time dependent density functional theory (TDDFT) calculations were performed to demonstrate the electronic properties of BTAC and its product, BTAC-O−. Finally, the probe was successfully applied for the fluorescence bioimaging of cysteine owing to its photostability and low cytotoxicity.

Risk prediction for oral potentially malignant disorders using fuzzy analysis of cytomorphological and autofluorescence alterations in habitual smokers

AIM This study aims to develop a novel noninvasive method for early cancer trend diagnosis in habitual smokers by corroborating cytomorphological and autofluorescence alterations. MATERIALS & METHODS A total of 120 subjects were included and categorized into nonsmoker, smoker and clinically diagnosed oral potentially malignant disorder (OPMD) patients. Oral exfoliative epithelial cells were studied through differential interference contrast and fluorescence microscopy. Fuzzy trend analysis was performed using measured parameters for determining the risk factors among smokers. RESULTS The risk assessment in this study showed a positive correlation of smoking duration with early cancer risk factors with a correlation co-efficient of 0.86. CONCLUSION Alterations in cellular morphology and autofluorescence intensities showed positive correlation with OPMD. The present study will benefit to investigate early prediction of OPMD among susceptible individuals.

Autofluorescence signatures for classifying lung cells during epithelial mesenchymal transition

The cellular mechanism of epithelial mesenchymal transition (EMT) has been observed to play a pivotal role in embryogenesis, wound healing and cancer metastasis. This fundamentally dynamic phenomenon requires a multifaceted appreciation to evaluate its role in cancer progression. The present study documents alterations in the endogenous fluorescence signatures of lung cells (normal and cancer) to classify them during the progression of EMT and reports their association with cytomorphological and cytoskeletal attributes. Cellular endogenous red and green fluorescence showed a gradual increase during the progression of EMT while the blue component showed the reverse effect. Furthermore, randomness in F-actin fibrillar arrangement was notably elevated and its expression increased. Altered cell shape with heightened vimentin expression was also documented. Principal component analysis (PCA), an unsupervised classifier, was effectively employed endorsing these multi-level attributes to visualize EMT progression. Dimensionality reduction was further carried out to elucidate the significance of autofluorescence. Red fluorescence had the greatest contribution in differentiating cells during the transition. The features were re-evaluated using another in-house built binary classifier, namely vector valued regularized kernel approximation (VVRKFA), in order to understand EMT progression. Gradual increase in classification accuracy with EMT progression indicated cellular changes in the above-mentioned features. Logical corroboration of the findings suggested strong connections between cellular shape and cytoskeletal attributes with autofluorescence phenomena during EMT.

Reaction-based ratiometric fluorescent probe for selective recognition of sulfide anions with a large Stokes shift through switching on ESIPT

An ESIPT-based, highly selective, ratiometric fluorescent probe BNPT has been synthesized and characterized, which shows turn-on fluorescence response in the presence of S2−, attributed to the removal of a protective 2,4-dinitrobenzene (DNB) moiety, and the resulting fluorescent product has been used for the selective detection of Zn2+. UV-vis and fluorescence spectroscopy analysis, and DFT and TDDFT calculations were carried out to understand the sensing mechanism. The probe BNPT displays a rapid response time and good sensitivity. The probe can detect quantitatively in a concentration range of 0–6.0 μM. The detection limit is 31.3 nM. The sensing ability of BNPT has been successfully applied in real water samples. Applicability as an in-field test kit has been demonstrated by sensing with a BNPT-coated TLC plate. The probe BNPT has been successfully used for visualization of intracellular environment in living cells. The uniqueness lies in the fact that starting with the probe BNPT, sensing can be achieved by two different mechanisms – first, by selective de-protection of the probe BNPT and second, by reacting with the Zn2+ ensemble with S2−.

Repositing honey incorporated electrospun nanofiber membranes to provide anti-oxidant, anti-bacterial and anti-inflammatory microenvironment for wound regeneration

AbstractTopical application of honey for tissue regeneration, has recently regained attention in clinical practice with controlled studies affirming its efficacy and indicating its role in regeneration over repair. Parallely, to overcome difficulties of applying raw honey, several product development studies like nanofibrous matrices have been reported. However, one approach concentrated on achieving highest possible honey loading in the nanofiber membranes while other studies have found that only specific honey dilutions result in differential cellular responses on wound healing and re-epithelization. From these results, it can be suggested that high honey loading provides optimum external microenvironment, low-loaded membranes could provide a more conducive internal microenvironment for tissue regeneration. With this hypothesis, this paper sought to evaluate ability of low-honey loaded nanofibers to modulate the anti-oxidant, anti-biofilm and anti-inflammatory properties which are important to be maintained in wound micro-environment. A loading-dependent reduction of biofilm formation and anti-oxidant activity was noted in different concentration ranges investigated. After scratch assay, a certain honey loading (0.5%) afforded the maximum re-epithelization. Since there is lack of methods to determine anti-inflammatory properties of nanofiber membranes during epithelial healing process, we performed anti-inflammatory assessment of nano-fibers by evaluating the expressions of pro-inflammatory markers-Cycloxygenase-2 (COX-2) and Interleukin-6 (IL-6) and to confirm the optimized concentration. Considering the role of COX-2 and IL-6, the novel methodology used in this study can also be developed as an assay for anti-inflammatory matrices for wound healing.

A PET based fluorescent chemosensor with real time application in monitoring formaldehyde emissions from plywood

An easily synthesized (7-nitrobenz-2-oxa-1,3-diazole) NBD piperazine conjugate, NPC, has been successfully employed for the fluorogenic sensing of the hazardous substance, formaldehyde (FA), based on the inhibition of photoinduced electron transfer (PET) as a consequence of formimine creation, which was proven by ESI-MS analysis. The probe has been found to be highly selective with a low response time of 2 min. The robust sensor NPC has been used to demonstrate its practical applicability in detecting vapor phase FA through emissions from plywood samples. The cell permeability has also been exploited to demonstrate the possibility of intracellular FA estimation using this probe.

A Perylene diimide based fluorescent probe for caffeine in aqueous medium

ABSTRACT Caffeine is a legal stimulant drug which has received considerable attention due to its widespread use as a beverage and in pharmaceutical formulations. However, reported chemosensors for caffeine are limited. In the present study use of a perylene diimide (PDI) derivative has been explored for the first time for detection and quantification of caffeine in an aqueous medium. Spectroscopic studies (UV-Vis, Fluorescence, FTIR and 1H-NMR) suggest that aspartic acid modified perylene diimide (PASP) may bind to caffeine through π-π interaction. This interaction results in immediate quenching of fluorescence and optical color change which can be perceived through naked eyes. This probe has been successfully used for bio-imaging of caffeine in living cells. Graphical Abstract

Reaction-based bi-signaling chemodosimeter probe for selective detection of hydrogen sulfide and cellular studies

A new quinoline-indolium-based chemical probe (DPQI) was synthesized and characterized for selective detection of hydrogen sulphide (H2S). Probe DPQI displays highly selective and sensitive detection of hydrogen sulphide over other allied anions and thiol-containing amino acids in aqueous-DMSO at physiological pH. The probe DPQI acts as a bi-signaling fluorescent chemodosimeter for selective detection of hydrogen sulphide when excited at different wavelengths. The selectivity was guaranteed by the use of the unique nucleophilicity of HS− for nucleophilic addition to the most electrophilic positively charged centre followed by thiolysis of the dinitrophenyl ether to yield DNB-SH and a fluorescent phenoxide moiety, which led to the fluorescence emission ‘turn on’ and characteristic visual fluorescent color change behavior of the sensing system. This is why the probe DPQI showed different optical properties at varying concentrations of hydrogen sulphide. The structural and electronic properties of the probe (DPQI) and its thiolysis product have been demonstrated using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. Utilizing this probe, we have successfully detected hydrogen sulphide in live cells.