Debdutta Ray

Bio: Debdutta Ray is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Pentacene & Charge carrier. The author has an hindex of 4, co-authored 10 publication(s) receiving 37 citation(s). Previous affiliations of Debdutta Ray include Indian Institutes of Technology.

Enhancing the sensitivity of point-of-use electrochemical microfluidic sensors by ion concentration polarisation – A case study on arsenic

Abstract: Point of use (POU) sensors are extremely relevant, being capable of providing fast and reliable analysis in remote and resource-limited settings. Of all the diverse techniques utilised for POU sensors, a combination of electrochemistry and microfluidics may have the greatest potential towards quantitative assessment of heavy metal ions. The major challenge in combining these for sensing applications lies in the complexity of fabricating integrated devices and the insufficient quantity of analytes in the sample volume. To address these issues, we have developed a radial microfluidic device capable of electrokinetic preconcentration by ion concentration polarization (ICP) and integrated it with electroactive surfaces. The proposed sensor is the first demonstration of concentration of heavy metal ions by ICP and its quantitative assessment by voltammetry. Utilising the integrated sensor, we have shown the sensing of As3+ down to 1 ppb by linear sweep voltammetry with ∼40 μL of sample. The sensor was also tested successfully for sensing As3+ in a field sample from an arsenic affected region of India. The sensor was also tested for the detection of other metal ions too. This work would facilitate the development of highly sensitive POU hand-held sensors for water quality monitoring in resource-limited areas.

Dual Probe Sensors Using Atomically Precise Noble Metal Clusters

Abstract: This article adds a new direction to the functional capability of protein-protected atomically precise gold clusters as sensors. Counting on the extensively researched intense luminescence of these clusters and considering the electron donating nature of select amino acids, we introduce a dual probe sensor capable of sensing changes in luminescence and conductivity, utilizing bovine serum albumin-protected atomically precise gold clusters hosted on nanofibers. To this end, we have also developed a hybrid nanofiber with a conducting core with a porous dielectric shell. We show that clusters in combination with nanofibers offer a highly selective and sensitive platform for the detection of trace quantities of trinitrotoluene, both in solution and in the vapor phase. In the solution phase, trinitrotoluene (TNT) can be detected down to 1 ppt at room temperature, whereas in vapor phase, 4.8 × 109 molecules of TNT can be sensed using a 1 mm fiber. Although the development in electrospinning techniques for fabri...

Determination of the width of the density of states of the highest occupied molecular orbital in pentacene

Abstract: We present a simple and effective method to estimate the width (σ) of the density of states (DOS) of the Highest Occupied Molecular Orbital (HOMO) in pentacene using field effect studies. This method can be applied to most organic semiconductors where charge carrier motion is by thermally activated hopping. The charge carrier density dependent mobility acts as the probe. We show from simulations that the variation of mobility, as a function of charge carrier density, is highly sensitive to σ. Thus, σ can be found with low error using this method. We optimize the fabrication process to develop pentacene transistors with greatly diminished non-idealities. We estimate the width of the DOS of the HOMO for pentacene to be 80 ± 10 meV. The contribution of the tail states is explored and we find it to be negligible in the on-state of the transistors studied.

Study of exciton-polaron interaction in pentacene field effect transistors using high sensitive photocurrent measurements

Abstract: Luminescence quenching in the presence of polarons is one of the major challenges in organic light emitting devices. In this work, exciton quenching in the presence of polarons is studied using phase sensitive photocurrent measurements on pentacene field effect transistors. The enhancement of conduction in the organic field effect transistors on light illumination is studied using photocurrent spectral response measurements and corresponding optical simulations. The photocurrent is shown to be governed by the polaron mobility and the exciton quenching efficiency, both of which depend on the polaron density in the channel. Two models are proposed on the exciton dynamics in the presence of gate induced polarons in the transistor channel. The first model simulates the steady-state exciton concentration profile in the presence of exciton-polaron interaction. The second one is a three-dimensional steady state exciton-polaron interaction model, which supports the findings from the first model. It is shown that the excitons quench by transferring its energy to polarons, thereby promoting the latter to high energy states in the density of states manifold. The polarons move in the higher energy states with greater microscopic mobility before thermalizing, thereby leading to an enhancement of conduction. It is observed that for the present system, where charge carrier transport is by hopping, all polarons interact with excitons. This implies that for low mobility systems, the interaction is not limited to deep trapped polarons.

Organic field effect transistors (OFETs) of poly(p-phenylenevinylene) fabricated by chemical vapor deposition (CVD) with improved hole mobility

Abstract: This study demonstrates organic field effect transistors (OFETs) of chemical vapor deposited poly(p-phenylenevinylene) (PPV). The optical and electrical properties of the films are reported. It is found that the grain sizes of the film can be engineered by surface treatment of the oxide of the Si/SiO2 substrate in the transistor with a self assembled monolayer (SAM) of octadecyltrichlorosilane (OTS). The enhancement of domain sizes of the grains with surface treatment leads to an increase in hole mobility to 1.4 × 10−4 cm2/V s, which is 1000 times higher than that reported for solution processed PPV field effect transistors. A comparison of the hole mobility between CVD grown PPV films and those reported for PPV and its derivatives, grown by spin coating or drop casting, shows that CVD provides an optimized alternative for growth of devices. It is shown that a low annealing temperature of 180 °C is enough to achieve polymerization. Film deposition by CVD has the advantage that up-scaling, with a fine control on the film thickness, is possible without compromising on the electrical/morphological properties. A vacuum based method of polymer deposition opens up the prospect of hybrid devices based on small molecules and polymers.

Naphthoquinone-Dopamine Linked Colorimetric and Fluorescence Chemosensor for Selective Detection of Sn2+ Ion in Aqueous Medium and Its Bio-Imaging Applications

Abstract: A simple naphthoquinone–dopamine hybrid (2CND) was designed and fabricated as a colorimetric and fluorescence chemosensor for the selective recognition of Sn2+ in the aqueous medium. This simply ac...

Appearance of SERS activity in single silver nanoparticles by laser-induced reshaping.

Abstract: We report simultaneous plasmonic scattering and Raman spectroscopic observations of single citrate capped silver nanoparticles (AgNPs) which exhibit surface enhanced Raman scattering (SERS) upon meeting specific conditions induced by laser (532 nm) exposure. We show that nanoparticles which are not initially SERS active become SERS active by laser-induced reshaping/reorientation. A set-up developed for these observations enabled in situ high speed time-lapse characterization using plasmonic and Raman spectroscopies in conjunction with dark-field microscopy (DFM). Changes in the AgNPs were confirmed by monitoring plasmonic scattering spectra and DFM images. Time-lapse observations have shown that laser-induced changes in the plasmonic properties of AgNPs resulted in the appearance of SERS. Spectral matching between plasmon resonance and downward molecular vibronic transitions for molecules adsorbed on the surface of plasmonic nanomaterials is attributed to the nanoparticle SERS. We have further shown that the release of silver ions by silver nanoparticles can be the probable reason for their plasmonic changes. Gold nanoparticles inert to such mild (850 μW, 532 nm) laser-induced changes do not exhibit the appearance of SERS.

Mitochondria-targeted dual-channel colorimetric and fluorescence chemosensor for detection of Sn2+ ions in aqueous solution based on aggregation-induced emission and its bioimaging applications.

Abstract: Several fluorescence and colorimetric chemosensory for Sn2+ detection in an aqueous media have been reported, but applications remain limited for discriminative Sn2+ detection in live human cells and zebrafish larvae. Herein, a mitochondria-targeted Sn2+ “turn-on” colorimetric and fluorescence chemosensor, 2CTA, with an aggregation-induced emission (AIE) response was developed. The sensing of Sn2+ was enabled by a reduction-enabled binding pathway, with the conversion of –C˭O groups to –C–OH groups at the naphthoquinone moiety. The color changed from light maroon to milky white in a buffered aqueous solution. The chemosensor 2CTA possessed the excellent characteristics of good water solubility, fast response (less than 10 s), and high sensitivity (79 nM) and selectivity for Sn2+ over other metal ions, amino acids, and peptides. The proposed binding mechanism was experimentally verified by means of FT-IR and NMR studies. The chemosensor 2CTA was successfully employed to recognize Sn2+ in live human cells and in zebrafish larvae. In addition, a colocalization study proved that the chemosensor had the ability to target mitochondria and overlapped almost completely with MitoTracker Red. Furthermore, a bioimaging study of live cells demonstrated the discriminative detection of Sn2+ in human cancer cells and the practical applications of 2CTA in biological systems.

Nano-Enabled sensors for detection of arsenic in water

Abstract: The elevated cases of arsenic contamination reported across the globe have made its early detection and remediation an active area of research. Although, the World Health Organisation has set the maximum provisional value for arsenic in drinking water at 10 parts per billion, yet concentrations as high as 5000 parts per billion are still reported. In human beings, chronic arsenic exposure can culminate into lethal diseases such as cancer. Thus, there is a need for urgent emergence of efficient and reliable detection system. This paper offers an overview of the state-of-art knowledge on current arsenic detection mechanisms. The central agenda of this paper is to develop an understanding into the nano-enabled methods for arsenic detection with an emphasis on strategic fabrication of nanostructures and the modulation of nanomaterial chemistry in order to strengthen the knowledge into novel nano-enabled solutions for arsenic contamination. Towards the end prospects for arsenic detection in water are also prompted.