BITS Faculty Publications
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Item A carbon quantum dot and rhodamine-based ratiometric fluorescent complex for the recognition of histidine in aqueous systems(RSC, 2019-01) Sidhu, Jagpreet SinghHistidine is an essential α-amino acid that plays a crucial role in tissue development and helps in the transmission of metallic ions during biological events. However, an abnormal level of histidine in the body is associated with various physiological conditions such as arthritis, liver cirrhosis, kidney diseases, and asthma. Herein, a unique ratiometric fluorescence sensing system has been developed for the recognition of histidine. The sensing system was developed using carbon quantum dots (CQDs) as an energy donor and a rhodamine 6G derivative (HS30) as an energy acceptor unit. Interestingly, upon the addition of Fe(III) into the mixture of CQDs and HS30, the phenomenon of fluorescence resonance energy transfer (FRET) was observed when excited at 350 nm. The emergence of a strong emission peak at 551 nm on the addition of Fe(III) suggested the formation of a ratiometric fluorescent complex “CQDs–Fe–HS30”. The ratiometric behavior of “CQDs–Fe–HS30” was studied by monitoring fluorescence emissions at 425 nm and 551 nm with an excitation wavelength of 350 nm. Furthermore, “CQDs–Fe–HS30” was employed for the recognition of histidine in an aqueous system. Due to the high affinity of histidine to Fe(III), the addition of histidine to an aqueous solution of “CQDs–Fe–HS30” resulted in the displacement of the Fe(III) cation from the complex, and the simultaneous quenching and enhancement of the emission peaks at 551 nm and 425 nm, respectively, was observed. The developed sensing system was successfully employed for a histidine recovery experiment in human urine samples with satisfactory results. Furthermore, the mixture of CQDs and HS30 was successfully utilized to implement an inhibit logic gate with Fe(III) and histidine as inputs and emission at 551 nm as output.Item The Photochemical Degradation of Bacterial Cell Wall Using Penicillin-Based Carbon Dots: Weapons Against Multi-Drug Resistant (MDR) Strains(Wiley, 2017-10) Sidhu, Jagpreet SinghInability of antibiotics repertoire to effectively control the progress of multi-drug resistant (MDR) bacteria has prompted the substantial curiosity among the scientists to seek new tactics to combat the bacterial growth. Therefore, to eradicate the pathogenic bacteria with least cytotoxicity, we employed carbon dots as a broad spectrum of antibacterial weapons in the presence of visible light. Instead of using citric acid, we engaged the penicillin G as a carbon source for the synthesis of penicillin carbon dots (PCDs), which made the carbon dots more aggressive towards pathogenic microbes. Penicillin was also covalently attached to –NH2 containing citric acid based CDs (CDs-Penicillin) via an amide bond to evaluate whether penicillin in the form of PCD has retained its activity or in its conjugated form (CDs-Penicillin). Synthesized dots were assessed for their antibacterial activity against Staphylococcus aureus, Escherichia coli (DH5α), MDR Escherichia coli and Methicillin-resistant Staphylococcus aureus in the presence as well as the absence of visible light. The mechanism of bacteria-killing through cell wall rupturing was investigated using scanning electron microscopy. Antibacterial assay demonstrates that penicillin in the form of PCDs retained its activity and possess great prospects in the development of new bactericidal therapies to invade the MDR bacteria. Cytotoxicity of both PCDs and CDs-Penicillin has been evaluated by measuring the viability of human HeLa cells. Fluorescence images of bacteria collected using different excitation wavelength.