Sameer Hussain

Vapor phase sensing of ammonia at the sub-ppm level using a perylene diimide thin film device

The fabrication of a two terminal sensor device based on a histidine substituted perylene diimide (PDI-HIS) thin film for the sensitive detection and quantification of ammonia (NH3) vapors by monitoring the changes in its current intensity is reported at room temperature under ambient conditions. The thin film morphological variations of the drop cast PDI-HIS films before and after exposure to NH3 vapors are characterized by FESEM and TEM confirming the diffusion/adsorption of the NH3 vapors. The solution cast PDI-HIS thin film gas sensor device exhibited rapid, highly sensitive and selective vapor phase response towards NH3 with a detection limit as low as 0.56 ppm which is much lower than the maximum permissible limit set for NH3 (25 ppm) for prolonged exposure. Furthermore, control sensing experiments performed using alkyl substituted PDI (PDI-n-octyl) demonstrated that the presence of histidine groups at the imide position of PDI-HIS drastically affects the solid-state aggregation mode as well as redox potential that ultimately enhances the sensing response of the device. The key performance parameters of the device such as sensitivity, response/recovery time, selectivity, recyclability, stability and detection limit demonstrated the protocol as simple, reliable, cost-effective and most efficient in performing NH3 detection under very realistic conditions.

Highly Precise Detection, Discrimination, and Removal of Anionic Surfactants over the Full pH Range via Cationic Conjugated Polymer: An Efficient Strategy to Facilitate Illicit-Drug Analysis

A water-soluble cationic conjugated polyelectrolyte (CPE), poly(1,4-bis(6-(1-methylimidazolium)-hexyloxy)-benzene bromide) (PMI) displays extraordinary stability over the full pH range of 1-14 as well as in seawater, brine, urine, and other solutions and carries out efficient detection, discrimination, and removal of moderately dissimilar anionic surfactants (viz., sodium dodecyl benzenesulfonate (SDBS) and sodium dodecyl sulfate (SDS)) at very low levels (31.7 and 17.3 parts per billion (ppb), respectively). PMI formed stable hydrogels in the presence of SDS that remained unaffected by strong acids/bases, heating, ultrasonication, or exposure to light, whereas SDBS formed precipitate with PMI as a result of its different interpolymer cofacial arrangement via Columbic attraction. The complex-forming ability of PMI with SDS and SDBS facilitated their elimination from water or drug-doped urine samples without the use of any organic solvent, chromatographic technique, or solid support. This protocol, the first of its kind for the removal of anionic surfactants at very low concentrations from any type of solution and competitive environments, demonstrates an original application using a CPE. The surfactant-free sample solutions could be precisely analyzed for the presence of illicit drugs by any standard methods. Using PMI, a newly developed CPE, a rapid and practical method for the efficient detection, discrimination, and removal of SDS and SDBS at ppb levels from water and urine, under harsh conditions, and in natural chemical environments is demonstrated.

A rapid and sensitive detection of ferritin at a nanomolar level and disruption of amyloid β fibrils using fluorescent conjugated polymer

Enhanced levels of toxic metals, especially iron, from the labile iron pool in the brain are primarily responsible for the pathogenesis of several neurological disorders, such as Alzheimers disease (AD). These metals are a major source for generating highly toxic reactive oxygen species (ROS), accelerating amyloid β (Aβ) peptide aggregation in the brains of AD patients. Aβ has high affinity for iron, resulting in its accumulation and localization in brain plaques enhancing neurotoxic H2O2, oxidative stress and free radical formation. Hence, controlling neurotoxicity would also involve regulation of the redox-active metals present, along with the Aβ. Non toxic conjugated polymer (CP) poly(1,4-bis-(8-(8-hydroxyquinoline)-octyloxy)-benzene) (PHQ) binds iron containing heme and non-heme proteins, such as ferritin, at nanomolar levels with the highest known selectivity (a Stern–Volmer constant (Ksv) value of 0.84 × 107 M−1) in cerebrospinal fluid (CSF) and has been utilized to interact with the bound iron, including non-heme ferritin, in the Aβ protofibril aggregates and diminish their accumulation. The anti-AD activity of PHQ was confirmed via in vitro control studies by doping CSF of healthy individuals (H-CSF) with Aβ(1–40) with and without iron using a Thioflavin-T (ThT) binding assay test and electron microscopy analysis. This conceptually new strategy to clear the cerebral deposits using a CP allows the toxic aggregated Aβ peptide fibrils present in the CSF to be successfully disrupted under physiological conditions.

FRET-assisted selective detection of flavins via cationic conjugated polyelectrolyte under physiological conditions

Flavins viz. riboflavin (RF, vitamin B2), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) represent an important class of biomolecules ubiquitously found in living systems that are vital for numerous cellular activities inside the body. The fluorescence amplified detection of these flavins at ppb levels is achieved for the first time using water soluble cationic conjugated polymer PMI under physiological conditions. The substantial FRET, variable binding abilities of flavins with PMI via Columbic interaction and the subsequent displacement of FMN/FAD by simple chelating agent like Cu2+ affords a simple and consistent method to detect and discriminate them even in the presence of most common interfering analytes usually found in biosystems. This new strategy based on FRET provides more precise measurement using two different emission bands and hence, eliminates the environmental effects unlike in classical or direct fluorescence method. Furthermore, the determination of flavins in human blood serum using cationic conjugated polyelectrolyte PMI signifies the potential of this protocol in studying the metabolic processes and clinical assessment of diseases related to flavins.

Anion-Exchange Induced Strong π-π Interactions in Single Crystalline Naphthalene Diimide for Nitroexplosive Sensing: An Electronic Prototype for Visual on-Site Detection.

A new derivative of naphthalene diimide (NDMI) was synthesized that displayed optical, electrical, and visual changes exclusively for the most widespread nitroexplosive and highly water-soluble toxicant picric acid (PA) due to strong π-π interactions, dipole-charge interaction, and a favorable ground state electron transfer process facilitated by Coulombic attraction. The sensing mechanism and interaction between NDMI with PA is demonstrated via X-ray diffraction analysis, (1)H NMR studies, cyclic voltammetry, UV-visible/fluorescence spectroscopy, and lifetime measurements. Single crystal X-ray structure of NDMI revealed the formation of self-assembled crystalline network assisted by noncovalent C-H···I interactions that get disrupted upon introducing PA as a result of anion exchange and strong π-π stacking between NDMI and PA. Morphological studies of NDMI displayed large numbers of single crystalline microrods along with some three-dimensional (3D) daisy-like structures which were fabricated on Al-coated glass substrate to construct a low-cost two terminal sensor device for realizing vapor mode detection of PA at room temperature and under ambient conditions. Furthermore, an economical and portable electronic prototype was developed for visual and on-site detection of PA vapors under exceptionally realistic conditions.

One-pot synthesis of functionalized 4-hydroxy-3-thiomethylcoumarins: detection and discrimination of Co2+ and Ni2+ ions

A wide variety of 4-hydroxy-3-thiomethylcoumarin derivatives were synthesized through a one-pot three-component reaction from 4-hydroxycoumarin, aldehydes and thiols, catalysed by L-proline in ethanol at room temperature, in moderate to good yields. The present protocol offers many advantages such as milder reaction conditions, green solvent, easy work up procedure and requirement of a smaller amount of catalyst. Furthermore, one of the derivatives (30a) has been successfully employed as a “turn-off” fluorescence probe that displays remarkable changes in its optical properties only in the presence of cobalt and nickel ions in aqueous based media. The ligand (30a) showed high selectivity towards Co2+ & Ni2+ without any interference from other commonly coexisting metal ions. Fluorescence quenching of ligand (30a) by Co2+ & Ni2+ was found to be ∼80% and ∼85% respectively in 9 : 1 DMSO/HEPES buffer (pH = 7.4, 10 mM) at room temperature. Significant changes in the UV-vis spectra with a clear formation of isosbestic points confirms the formation of ligand–metal complexes. The predicted binding mode (2 : 1) for ligand–metal was observed from High Resolution Mass Spectroscopy, Jobs plots and single crystal X-ray structures of the complexes. The lower stability of the cobalt(II) complex than the nickel(II) complex provides a reliable platform to distinguish Co2+ from Ni2+ via a “turn-on” photoluminescence response towards the disodium salt of ethylenediaminetetraacetic acid (EDTA).