Review of Gold Nanoparticles in Surface Plasmon-Coupled Emission Technology: Effect of Shape, Hollow Nanostructures, Nano-Assembly, Metal-Dielectric and Heterometallic Nanohybrids.

Point-of-care (POC) diagnostic platforms are globally employed in modern smart technologies to detect events or changes in the analyte concentration and provide qualitative and quantitative information in biosensing. Surface plasmon-coupled emission (SPCE) technology has emerged as an effective POC diagnostic tool for developing robust biosensing frameworks. The simplicity, robustness and relevance of the technology has attracted researchers in physical, chemical and biological milieu on account of its unique attributes such as high specificity, sensitivity, low background noise, highly polarized, sharply directional, excellent spectral resolution capabilities. In the past decade, numerous nano-fabrication methods have been developed for augmenting the performance of the conventional SPCE technology. Among them the utility of plasmonic gold nanoparticles (AuNPs) has enabled the demonstration of plethora of reliable biosensing platforms. Here, we review the nano-engineering and biosensing applications of AuNPs based on the shape, hollow morphology, metal-dielectric, nano-assembly and heterometallic nanohybrids under optical as well as biosensing competencies. The current review emphasizes the recent past and evaluates the latest advancements in the field to comprehend the futuristic scope and perspectives of exploiting Au nano-antennas for plasmonic hotspot generation in SPCE technology.

Discovery of benzoxazole-thiazolidinone hybrids as promising antibacterial agents against Staphylococcus aureus and Enterococcus species.

Antibiotic resistance is rapidly exacerbating the unceasing rise in nosocomial infections caused by drug-resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Enterobacteriaceae (CRE) and vancomycin-resistant Enterococcus (VRE). Therefore, there is a dire need for new therapeutic agents that can mitigate the unbridled emergence of drug-resistant pathogens. In the present study, several benzoxazole-thiazolidinone hybrids (BT hybrids) were synthesized and evaluated for their antibacterial activity against the ESKAP pathogen panel. The preliminary screening revealed the selective and potent inhibitory activity of hydroxy BT hybrids against S. aureus with MIC ≤ 4 µg mL-1. Hydroxy compounds (BT25, BT26, BT18, BT12, and BT11) exhibited a good selectivity index (SI > 20), which were determined to be non-toxic to Vero cells. An engaging fact is that two compounds BT25 and BT26 showed potent activity against various clinically-relevant and highly drug resistant S. aureus (MRSA & VRSA) and Enterococcus (VRE) isolates. These hybrids showed concentration-dependent bactericidal activity that is comparable to vancomycin. These experimental results were corroborated with docking, molecular dynamics, and free energy studies to discern the antibacterial mechanisms of hydroxy BT hybrids with three bacterial enzymes DNA gyrase B, MurB, and penicillin binding protein 4 (PBP4). The reassuring outcome of the current investigation confirmed that the aforementioned BT hybrids could be used as very promisingly potent antibacterial agents for the treatment of Staphylococcus aureus and Enterococcus infections.

Smartphone-Based Attomolar Cyanide Ion Sensing Using Au-Graphene Oxide Cryosoret Nanoassembly and Benzoxazolium-Based Fluorophore in a Surface Plasmon-Coupled Enhanced Fluorescence Interface.

Photoplasmonic platforms are being demonstrated as excellent means for bridging nanochemistry and biosensing approaches at advanced interfaces, thereby augmenting the sensitivity and quantification of the desired analytes. Although resonantly coupled electromagnetic waves at the surface plasmon-coupled emission (SPCE) interface are investigated with myriad nanomaterials in order to boost the detection limits, rhodamine moieties are ubiquitously used as SPCE reporter molecules in spite of their well-known limitations. In order to overcome this constraint, in this work, a benzoxazolium-based fluorescent molecule, (E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]oxazol-3-ium iodide (DSBO), was synthesized to selectively detect the cyanide (CN-) ions in water samples. To this end, the sensitivity of the fabricated SPCE substrates is tested in spacer, cavity, and extended cavity nanointerfaces to rationalize the configurational robustness. The performance of the sensor is further improved with the careful engineering of gold (Au)-graphene oxide (GO) cryosoret nanoassemblies fabricated via an adiabatic cooling technology. The unique dequenching (turn-on) of the quenched (turn-off) fluorescent signal is demonstrated with the hybridized metal-π plasmon synergistic coupling in the nanovoids and nanocavities assisting delocalized Bragg and localized Mie plasmons. The spectro-plasmonic analysis yielded highly directional, polarized (>95%), and enhanced emission attributes with an attomolar limit of detection of 10 aM of CN- ions with high linearity (R2 = 0.996) and excellent reliability, in addition to an exceptional correlation with the theoretically obtained TFclac simulations. The CN- ion sensing is experimentally validated with the smartphone-based cost-effective SPCE detection technology to render the device amenable to resource-limited settings. We believe that the unique fluorophore-cryosoret nanoassemblage presented here encourages development of frugal, unconventional, and highly desirable strategies for the selective quantitation of environmentally and physiologically relevant analytes at trace concentrations for use in point-of-care diagnostics.

Graphitic Carbon Cloth-Based Hybrid Molecular Catalyst: A Non-conventional, Synthetic Strategy of the Drop Casting Method for a Stable and Bifunctional Electrocatalyst for Enhanced Hydrogen and Oxygen Evolution Reactions.

Hydrogen energy production through water electrolysis is envisaged as one of the most promising, sustainable, and viable alternate sources to cater to the incessant demands of renewable energy storage. Germane to our effort in this field, we report easily synthesizable and very cost-effective isoperthiocyanic acid (IPA) molecular complexes as electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under acidic and alkaline conditions. The Pd(II)IPA, Co(II)IPA, and Ni(II)IPA complexes were synthesized and were evaluated for HER and OER applications. These complexes when embedded onto graphitized carbon cloth (GrCC) exhibited a significant enhancement in the HER activity in contrast to their pristine counterparts. The hybrid electrocatalyst Pd(II)IPA among the three showed an extremely low overpotential of 94.1 mV to achieve a current density of 10 mA cm-2, while Co(II)IPA and Ni(II)IPA complexes showed overpotentials of 367 and 394 mV, respectively, to achieve a current density of 10 mA cm-2. These complexes on carbon cloth showed decreased charge transfer resistance compared to that of pristine metal complexes. The enhanced catalytic activity of the complexes on carbon cloth can be attributed to the porous and conducting nature of the graphitized carbon cloth. For OER activity, the Pd(II)IPA complex showed an excellent performance with an overpotential value of 210 mV, while Co(II)IPA and Ni(II)IPA exhibited overpotentials of 400 and 270 mV, respectively, to drive a current density of 10 mA cm-2 in 0.1 M KOH. This work further widens the scope and application of molecular complexes in combination with an excellent carbon support for renewable energy storage applications.

Design, synthesis and in silico screening of benzoxazole-thiazolidinone hybrids as potential inhibitors of SARS-CoV-2 proteases.

Hybrid molecules in the recent years have gained significant importance in drug research as promising therapeutic agents. We report a novel combination of two such bioactive scaffolds (benzoxazole and 4-thiazolidinone B-T hybrids) as inhibitors of SARS-CoV-2. The study uses an in silico approach to identify the potential of B-T hybrids as possible inhibitors of the SARS-CoV-2 proteases. Molecular docking was employed to identify the interactions of B-T hybrids with the two proteases - 3CLp (the 3-chymotrypsin-like protease) and PLp (the papain-like protease). Docking results of the screened 81 hybrids indicated that BT10 and BT14 interacted with the catalytic dyad residue of 3CLp (Cys145) with the best binding energy. MD simulations revealed that BT10 formed stable interactions via 4 hydrogen bonds with the catalytic site residues of 3CLp. In the case of PLp, BT27 and MBT9 interacted with the catalytic triad residue of PLp (His272) with high binding energy. MD simulations demonstrated that the reference drug Tipranavir relocated to the thumb region of the protease whereas BT27 remained in the active site of PLp stabilized by 2 hydrogen bonds, while MBT9 relocated to the BL2 loop of the palm region. The MM-PBSA and interaction entropy (IE) analysis indicated that BT14 exhibited the best ΔG (of -6.83 kcal mol-1) with 3CLp, while BT27 exhibited the best ΔG (of -7.76 kcal mol-1) with PLp. A four-step synthetic procedure was employed to synthesize the B-T hybrids starting from ammonium thiocyanate. The short-listed compounds in the case of 3CLp were synthesized and characterized using IR, NMR, and HRMS spectroscopic techniques.