Shweta Chopra

Selective chemosensing of spermidine based on fluorescent organic nanoparticles in aqueous media via a Fe3+ displacement assay

A novel fluorescent chemosensor based on fluorescent organic nanoparticles (F1) has been synthesized. This tripodal framework shows significant fluorescence quenching for Fe3+ ions from among nineteen metal ions due to the formation of a F1·Fe3+ complex. The lowest detectable concentration of F1 for Fe3+ ions was found to be 1.66 μM. Upon the addition of spermidine (a biologically active amine), the fluorescence intensity of the aqueous solution of complex increases with a detection limit of 3.68 μM indicating that spermidine can displace Fe3+ ions from the F1·Fe3+ complex. Moreover, the recognition of spermidine was selective with no interference from other biogenic amines studied. Thus, F1·Fe3+ acts as a potential sensor for spermidine through a cation displacement assay in aqueous media.

Fluorescent organic nanoparticles of tripodal receptor as sensors for HSO4− in aqueous medium: application to real sample analysis

A tripodal framework bearing mixed donor sites was synthesized using simple reactions and was used for sensor applications in an aqueous medium by subjecting it to a nano-aggregate (N1) formation using a re-precipitation method. The characteristic fluorescence profile of the receptor due to the naphthyl moiety was observed. N1 showed selective recognition behaviour towards HSO4− in aqueous medium with a good linear range of 0–65 μM. N1, the prepared nano-aggregates can be used to determine a lower concentration, as the detection limit for HSO4− ions in aqueous samples is 1.12 μM in a wide pH range; thus, making them appropriate for the use in environmental or biological samples.

Calix[4]arene based dipodal receptor nanohybrids for selective determination of chloride ions in aqueous media

A chemical sensor based on p-tert butyl calix[4]arene has been synthesized and characterized using an assortment of spectroscopic techniques such as (1)H NMR, (13)C NMR, and elemental analysis. For sensor application, organic nanoparticles (N1) of 1 have been primed by implementing re-precipitation technique, which were further employed for preparing organic-inorganic hybrid (H1) by decorating N1 with gold nanoparticles. Both N1 and H1 were characterized using UV-visible, fluorescence, and DLS studies. Photo-physical changes due to anion binding with H1 were scrutinized using UV-visible absorption spectrometer and found it to promptly and selectively recognize Cl(-) ions in aqueous media. Thus, H1 can be effectively used for recognition of Cl(-) ions in aqueous media over a wide pH range, in samples of real time importance with a detection limit of 2.84×10(-9) M with a linear detection range up to 50 μM.

Ultrasensitive and Selective Sensing of Selenium Using Nitrogen-Rich Ligand Interfaced Carbon Quantum Dots

This work reports a label-free, ultrasensitive, and selective optical chemosensory system for trace level detection of selenite (SeO32-), the most toxic form of selenium, in water. The probe, i.e., carbon quantum dots (CQDs), is designed from citric acid by means of pyrolysis and is interfaced with a newly synthesized nitrogen-rich ligand to create a selective sensor platform (functionalized CQDs, fCQDs) for selenite in a water matrix. Spectral (NMR, UV-vis, photoluminescence, Raman, and Fourier transform infrared analyses) and structural (high-resolution transmission electron microscopy) characteristics of the designed new probe were investigated. The developed sensor exhibits high sensitivity (limit of detection = 0.1 ppb), a wide detection range (0.1-1000 ppb range, relative standard deviation: 3.2%), and high selectivity even in the presence of commonly interfering ions reported to date, including Cl-, NO3-, NO2-, Br-, F-, As(V), As(III), Cu2+, Pb2+, Cd2+, Zn2+, Sr2+, Rb2+, Na+, Ca2+, Cs+, K+, Mg2+, Li+, NH4+, Co2+, etc. The observed selectivity is due to designed ligand characteristics in terms of strong Se-N chemistry. Ultrafast spectroscopic analysis of the fCQDs in the absence and presence of selenite was studied to understand the sensing mechanism. The sensor was successfully exemplified for real water samples and exhibits comparative performance to conventional ion channel chromatography as well as flame atomic absorption spectroscopy for selenite analysis. The promising results pave ways for realization of a field deployable device based upon a developed probe for selenite quantification in water.

Fe(III) conjugated fluorescent organic nanoparticles for ratiometric detection of tyramine in aqueous medium: A novel method to determine food quality

A tetrapodal receptor was synthesized and was processed into fluorescent organic nanoparticles (FONs) for determination of important analytes in aqueous medium. The receptor was fully characterized using characterization techniques. Recognition behavior of FONs towards different metal ions was investigated with fluorescence spectroscopy, amongst them Fe3+ ions showed quenching behavior in the emission spectra. The Fe3+ ion complex of FONs based sensor was further tested with different biogenic amines and ratiometric response was obtained for tyramine. Fluorescence emission profile of FONs. Fe3+ ion complex showed no change in the pH in wide range; thereby increasing their utility in biological and environmental samples. Tyramine detection was linearly proportional in response with the detection limit of 377 nM.

An organic–inorganic nanohybrid of a calix[4]arene based chromogenic chemosensor for simultaneous estimation of ADP and NADH

The versatility in the environmental and biological applications of nanohybrids encouraged us to prepare a novel chemosensor based on an organic–inorganic nanohybrid (H1) employing receptor 1 (R1), which was synthesized via the Schiff’s base condensation reaction of a calix[4]arene derivative and an aliphatic amine. Techniques such as DLS and TEM were employed for the characterization of organic nanoparticles (N1) and H1. Further, sensor properties of H1 were explored towards various biologically important molecules in aqueous media using UV-visible spectroscopy. The proposed sensor responded effectively for the selective and simultaneous nanomolar determination of adenosine diphosphate (ADP) and reduced nicotiniamide adenine dinucleotide (NADH). The response was not affected by the presence of each analyte or any other potentially interfering biomolecule or a high concentration of salt. The proposed sensor was also found to show a stable response in an extensive pH range thus widening its practical applicability. H1 was able to detect a minimum concentration (detection limit) of 6.11 × 10−9 M of ADP and 4.87 × 10−9 M of NADH. The prepared hybrid was subjected to real sample analysis for the determination of ADP and NADH in samples prepared artificially by adding known concentrations of NADH and ADP in solution and also in a mixture of both.

Chemosensors for biogenic amines and biothiols

There is burgeoning interest among supramolecular chemists to develop novel molecular systems to detect biogenic amines and bio-thiols in aqueous and non-aqueous media due to their potential role in biological processes. Biogenic amines are biologically important targets because of their involvement in the energy metabolism of human biological systems and their requirement is met through food and nutrition. However, the increasing instances of serious health problems due to food toxicity have raised the quality of food nowadays. Biogenic amines have been frequently considered as the markers or primary quality parameters of foods like antioxidant properties, freshness and spoilage. For instance, these amines such as spermine, spermidine, cadavarine, etc. may originate during microbial decarboxylation of amino acids of fermented foods/beverages. These amines may also react with nitrite available in certain meat products and concomitantly produce carcinogenic nitrosamine compounds. On the other hand, it is also well established that biothiols, particularly, thiol amino acids, provide the basic characteristics to food including flavor, color and texture that determine its acceptability. For instance, the reduction of thiol groups produces hydrogen sulfide which reduces flavour as in rotten eggs and spoiled fish, and the presence of hydrogen sulfide in fish is indicative of spoilage. Thus, biogenic amines and bio-thiols have attracted the profound interest of researchers as analytical tools for their quantification. Much scientific and technological information is issued every year, where the establishment of precise interactions of biogenic amines and bio-thiols with other molecules is sought in aqueous and non-aqueous media. This review summarizes the optical chemosensors developed for the selective detection of biogenic amines and bio-thiols.