A.K. Paul

Recent advances in the photovoltaic applications of coordination polymers and metal organic frameworks

Coordination polymers and metal organic frameworks (CPs/MOFs) have attracted a great deal of attention in a variety of scientific fields due to their unique and intriguing structural properties. Photovoltaic applications of these porous polymers belong to a relatively new area of research. The current status of research on this subject amply highlights the usefulness of CPs/MOFs in improving the properties of next-generation photovoltaic devices (e.g., dye-sensitized solar cells). This review article was written to cover the recent advancements that have been achieved in this rapidly expanding area of research. It also compares and contrasts the energy conversion efficiencies in photovoltaic applications using different MOFs and other systems.

A label-free electrochemical immunosensor for the detection of cardiac marker using graphene quantum dots (GQDs)

A label-free immunosensor based on electrochemical impedance spectroscopy has been developed for the sensitive detection of a cardiac biomarker myoglobin (cMyo). Hydrothermally synthesized graphene quantum dots (GQDs) have been used as an immobilized template on screen printed electrodes for the construction of an impedimetric sensor platform. The GQDs-modified electrode was conjugated with highly specific anti-myoglobin antibodies to develop the desired immunosensor. The values of charge transfer resistance (Rct) were monitored as a function of varying antigen concentration. The Rct value of the immunosensor showed a linear increase (from 0.20 to 0.31kΩ) in the range of 0.01-100ng/mL cMyo. The specific detection of cMyo was also made in the presence of other competing proteins. The limit of detection for the proposed immunosensor was estimated as 0.01ng/mL which is comparable to the standard ELISA techniques.

Graphene modified screen printed immunosensor for highly sensitive detection of parathion

Due to indiscriminate use of pesticides, there is a growing need to develop sensors that can sensitively detect the trace amount of pesticides in food and water samples. Parathion, identified as an acetylcholinesterase inhibitor, had been one of the most widely used pesticides throughout the world. Symptoms of its poisoning are found to be diverse enough to include nausea, vomiting, diarrhea, muscle cramping/twitching, and shortness of breath. In this work, a graphene based impedimetric immunosensor has been fabricated and employed for highly sensitive and specific detection of parathion. The fabrication proceeded through the modification of the screen-printed carbon electrodes (SPE) with graphene sheets, followed by their functionalization with 2-aminobenzyl amine (2-ABA) via an electrochemical reaction. These amine functionalized graphene electrodes were then bio-interfaced with the anti-parathion antibodies. In the impedimetric mode, this biosensor detected parathion in a broad linear range, i.e. 0.1-1000ng/L with a very low limit of detection (52pg/L). It also showed high selectivity towards parathion in the presence of malathion, paraoxon, and fenitrothion. The viability of this biosensor was demonstrated by detecting parathion in real samples (e.g., tomato and carrot) and through cross-calibration against HPLC.

Graphene-gated biochip for the detection of cardiac marker Troponin I

We report lithium ion intercalation mediated efficient exfoliation of graphite to form monolithic graphene sheets which have subsequently been investigated for the development of highly sensitive label-free electrochemical detection platform for cardiac biomarker, Troponin I (cTnI). The spectroscopic and morphological analysis demonstrated the formation of defect free graphene sheets which were successfully employed to fabricate an inter-digited microdevice in a drain-source configuration on a silicon biochip. The graphene gated biochip functionalized with anti-cTnI antibodies used in label free detection of cTnI which exhibited an excellent sensitivity in the picogram range (~1 pg mL(-1)) for cTnI without the use of any enzymatic amplification that promises its potential applicability for bio-molecular detection in clinical diagnosis.

Biofunctionalized rebar graphene (f-RG) for label-free detection of cardiac marker troponin I

One-step microwave-assisted unscrolling of carbon nanotubes to form functionalized rebar graphene (f-RG) is reported. The well-characterized f-RG on an interdigitated electrode biochip in a FET configuration showed enhanced electronic properties, as demonstrated with I-V characteristics. The developed device was biofunctionalized with specific anti-cTnI antibodies exhibiting a shift of threshold voltage from -2.15 V to -0.5 V and decrease in electron mobility from 3.609 × 10(4) to 8.877 × 10(3) cm(2) V(-1) s(-1). The new sensing strategy holds great promise for its applicability in diagnostics exhibiting high sensitivity (∼ 1 pg/mL) and specificity toward cardiac marker (cTnI).

One step in-situ synthesis of amine functionalized graphene for immunosensing of cardiac marker cTnI

2-Aminobenzyl amine (2-ABA) functionalized graphene is proposed for the ultrasensitive immunosensing of Cardiac Troponin I (cTnI). 2-ABA was electrochemically polymerized on the graphene decorated interdigitated electrode to obtain the amine functionalized graphene (f-GN). The f-GN electrode was then modified with monoclonal anti-cTnI antibodies via Schiff reaction based chemistry. Detailed characteristics of the processes involved and the finally developed antibody conjugated f-GN interdigitated electrode have been studied. The above micro-device was used in a drain source configuration for the sensing of cTnI. A wide dynamic linear range of antigen detection (0.01-1ng/mL) is achieved with the limit of detection of 0.01ng/mL. The utility of the proposed sensing technique is demonstrated by successfully testing the antigen concentration in spiked serum samples.

A luminescent nanocrystal metal organic framework for chemosensing of nitro group containing organophosphate pesticides

A luminescent nanocrystal metal–organic framework (NMOF1) of [Cd(atc)(H2O)2]nhas been synthesized by the reaction of Cd(II) ions with the sodium salt of H2atc (2-aminoterephthalic acid) in aqueous solution. The obtained fluorescent porous material has been characterized by X-ray diffraction, transmission electron microscopy, confocal microscopy, UV-visible spectroscopy, photoluminescence spectroscopy and surface area analysis. The synthesized NMOF1 exhibits reasonably good fluorescence characteristics (excitation wavelength = 340 nm, emission wavelength = 436 nm). The potential of the above Cd(II) based nanocrystal metal–organic framework (NMOF1) for the sensing of the nitroaromatic-containing organophosphate pesticides (nitro OPs) parathion, methyl parathion, paraoxon and fenitrothion is demonstrated. It has been possible to detect the above four OPs separately in the concentration range of 1–500 ppb. The detection limit of the proposed method for all the said OPs is 1 ppb. Interestingly, their mixture also shows the above characteristic data. The proposed method for the sensing of nitro OPs is also selective towards other OPs such as malathion, dichlorvos and monocrotophos.

Nanocomposite of europium organic framework and quantum dots for highly sensitive chemosensing of trinitrotoluene

Luminescent metal-organic frameworks (MOFs) are considered as next-generation sensor materials for small molecules and explosives. In the present work, a nanocomposite of luminescent europium organic framework (EuOF) and CdSe quantum dots (QDs) has been first time investigated for photoluminescence (PL) based highly sensitive detection of trinitrotoluene (TNT). The nanocomposite EuOF/QD has been synthesized by initiating the growth of EuOF in the presence of QDs. The successful synthesis of the product has been verified with the help of electron microscopy, X-ray diffraction analysis, and surface area measurements. Compared to EuOF alone, the EuOF/QD nanocomposite offers reproducible and stable measurements. The linear range of PL quenching based detection of TNT with EuOF/QD nanocomposite is 5-1000 ppb with the detection limit of 3 ppb. The detection of TNT with EuOF/QD is selective with respect to some other investigated aromatic compounds, such as phenol, o-cresol, toluene, benzene, nitrobenzene and nitrophenol.

Plasma etch models based on different plasma chemistry for micro-electro-mechanical-systems application.

The suitability of different plasma etch models based on various plasma chemistry has been evaluated for the fabrication of micro-mechanical structures and micro-electro-mechanical systems. Different etch models have been described for silicon etching based on fluorine and chlorine chemistry and the mechanisms involved in SiO2 etching. Conventional planar reactive ion etching systems have been utilized for the etching of SiO2 and silicon based on fluorine and chlorine etch models. Fluorine containing gases such as CHF3 in combination with Ar have been used for SiO2 etching and achieved nearly vertical sidewalls with smooth bottom surface. Gas mixtures such as SF6/O2 at low substrate temperatures and Cl2/BCl3 have been used for silicon etching and sidewall passivation techniques have been employed to achieve vertical sidewalls. The usefulness of chlorine chemistry using BCl3 gas chopping technique for the fabrication of high aspect ratio structures has been demonstrated.

Biological applications of zinc imidazole framework through protein encapsulation

The robustness of biomolecules is always a significant challenge in the application of biostorage in biotechnology or pharmaceutical research. To learn more about biostorage in porous materials, we investigated the feasibility of using zeolite imidazolate framework (ZIF-8) with respect to protein encapsulation. Here, bovine serum albumin (BSA) was selected as a model protein for encapsulation with the synthesis of ZIF-8 using water as a media. ZIF-8 exhibited excellent protein adsorption capacity through successive adsorption of free BSA with the formation of hollow crystals. The loading of protein in ZIF-8 crystals is affected by the molecular weight due to diffusion-limited permeation inside the crystals and also by the affinity of the protein to the pendent group on the ZIF-8 surface. The polar nature of BSA not only supported adsorption on the solid surface, but also enhanced the affinity of crystal spheres through weak coordination interactions with the ZIF-8 framework. The novel approach tested in this study was therefore successful in achieving protein encapsulation with porous, biocompatible, and decomposable microcrystalline ZIF-8. The presence of both BSA and FITC–BSA in ZIF-8 was confirmed consistently by spectroscopy as well as optical and electron microscopy.