Vaibhavkumar N. Mehta

One-pot green synthesis of carbon dots by using Saccharum officinarum juice for fluorescent imaging of bacteria (Escherichia coli) and yeast (Saccharomyces cerevisiae) cells.

We are reporting highly economical plant-based hydrothermal method for one-pot green synthesis of water-dispersible fluorescent carbon dots (CDs) by using Saccharum officinarum juice as precursor. The synthesized CDs were characterized by UV-visible, fluorescence, Fourier transform infrared (FT-IR), dynamic light scattering (DLS), high-resolution transmission electron microscopic (HR-TEM), and laser scanning confocal microscopic techniques. The CDs are well dispersed in water with an average size of ~3 nm and showed bright blue fluorescence under UV-light (λex=365 nm). These CDs acted as excellent fluorescent probes in cellular imaging of bacteria (Escherichia coli) and yeast (Saccharomyces cerevisiae).

Preparation of multicolor emitting carbon dots for HeLa cell imaging

We have synthesized biocompatible fluorescent carbon dots (CDs) by a one-step hydrothermal method using Solanum tuberosum (potato) as a raw material. The CDs were characterized by UV-visible, fluorescence, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS) and high-resolution transmission electron microscopic (HR-TEM) techniques. We found that the carbonization of potato at ∼170 °C for 12 h produces highly fluorescent CDs of 0.2–2.2 nm size. The synthesized CDs are well dispersed in water and exhibited strong blue and bright blue emissions under UV illumination (λex = 302, 365 nm). The CDs showed a strong emission peak at 455 nm at an excitation wavelength of 374 nm. The CDs acted as fluorescent probes for multicolor (blue, green and red) imaging of HeLa cells and the CDs did not induce cell death, which indicates that the CDs are biocompatible and nontoxic to HeLa cells. Therefore, the CDs can be used as probes for cell-imaging applications in vitro and in vivo.

Dopamine dithiocarbamate functionalized silver nanoparticles as colorimetric sensors for the detection of cobalt ion

A colorimetric assay has been developed for facile, rapid and sensitive detection of Co2+ using dopamine dithiocarbamate functionalized silver nanoparticles (DDTC-Ag NPs) as a colorimetric sensor based on unique surface plasmon resonance properties. The presence of Co2+ induces the aggregation of Ag NPs through coordinate covalent bonds between the catechol groups of DDTC on the surface of Ag NPs and cobalt ions, resulting in a color change from bright yellow to reddish. These color changes are measured by UV-vis spectrophotometry, and can be directly read out with the naked eye. For the detection, UV-visible absorption spectra were measured by the absorbance ratio A570nm/A390nm. Under the optimum conditions, the analytical response was linear over the range from 1.0 mM to 15 mM (R2 = 0.993) with a detection limit of 14 μM. The proposed DDTC-Ag NPs-based colorimetric method is simple and sensitive for the detection of cobalt ions and allows for the monitoring of cobalt ions directly with naked eye.

Sensitive and selective colorimetric sensing of Fe3+ ion by using p-amino salicylic acid dithiocarbamate functionalized gold nanoparticles

We have developed a selective and sensitive colorimetric method for determination of Fe3+ ion by using p-amino salicylic acid dithiocarbamate functionalized gold nanoparticles (DTC-PAS-Au NPs) as colorimetric probes. The DTC-PAS-Au NPs were characterized by FT-IR, 1H NMR, UV-visible spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and atomic force microscopic (AFM) techniques, respectively. The DTC-PAS-Au NPs are aggregated rapidly by addition of Fe3+ ions, yielding a color change from red to blue. The characteristic surface plasmon resonance (SPR) peak (520 nm) of DTC-PAS-Au NPs was shifted to longer wavelength, 700 nm, which confirms the ligand-to-metal charge transfer between DTC-PAS-Au NPs and Fe3+ ions. Under the optimal conditions, a good linear relationship (correlation coefficient R2 = 0.993) was obtained between the ratio of the extinction at 700 nm to that at 520 nm and the concentration of Fe3+ over the range of 40–80 μM, with a detection limit of 14.82 nM. The DTC-PAS-Au NPs acted as colorimetric sensors for the selective detection of Fe3+ ions in real samples (blood and urine samples).

Malonamide dithiocarbamate functionalized gold nanoparticles for colorimetric sensing of Cu2+ and Hg2+ ions

In this study, a colorimetric probe was developed based on malonamide dithiocarbamate functionalized gold nanoparticles (MA–DTC–Au NPs) for the simultaneous colorimetric detection of Cu2+ and Hg2+ ions. The MA–DTC–Au NPs quickly aggregated in the presence of Cu2+ and Hg2+ ions, resulting in a color change from red to blue and a red-shift in their surface plasmon resonance peak (SPR) from 525 to 780 nm and to 680 nm for Cu2+ and Hg2+ ions, respectively. On the basis of this, the concentration of Cu2+ and Hg2+ ions can be visualized with the naked eye and can be quantitatively determined by UV-visible spectroscopy. The absorption ratios A780 nm/A525 nm and A680 nm/A525 nm show linear relationships with Cu2+ and Hg2+ ion concentrations within concentration ranges from 0.01 to 5 and 0.01 to 10 μM. The detection limits are as low as 41 nM and 45 nM for Cu2+ and Hg2+ ions, respectively. The MA–DTC–Au NPs were used as a potential colorimetric probe for the rapid, selective and sensitive detection of Cu2+ and Hg2+ ions in environmental water samples (drinking, tap, canal and river water).

Recent developments of liquid-phase microextraction techniques directly combined with ESI- and MALDI-mass spectrometric techniques for organic and biomolecule assays

The development of rapid, simple and reduced solvent consumption techniques for sample preparation is important for the isolation and preconcentration of organic and biomolecules from complex matrices. Miniaturized solvent-based extraction techniques have been intensively applied as sample pretreatment tools for the preconcentration of biomolecules from biological samples prior to their identification by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). This review provides an overview of miniaturized solvent extraction methods and their efficient extraction of trace or ultra-trace analytes and their identification by MALDI-MS. We discuss the recent developments of miniaturized liquid-phase extraction approaches, such as liquid-phase microextraction (LPME) and single-drop microextraction (SDME) techniques, for organic and biomolecule pretreatment prior to MALDI-MS analysis. We also provide an update on the state-of-the-art and promising prospects of LPME techniques directly combined with ESI- and MALDI-MS techniques for the analysis of trace levels of organic and biomolecules in complex matrices. We also outline the advances of using liquid microjunction surface sampling probes coupled with MS for trace level analyte assays. Nanoparticle-assisted microextraction coupled with MALDI-MS for organic and biomolecule analysis, and the future trends of potential LPME applications are also highlighted.

Functionalization of silver nanoparticles with 5-sulfoanthranilic acid dithiocarbamate for selective colorimetric detection of Mn2+ and Cd2+ ions

In this work, we have described the use of sulfoanthranilic acid dithiocarbamate functionalized silver nanoparticles as a probe for simple, rapid and simultaneous colorimetric detection of Mn2+ and Cd2+ ions. The Mn2+ and Cd2+ ions induce the aggregation of sulfoanthranilic acid dithiocarbamate functionalized silver nanoparticles, resulting in a color change from yellow to orange associated with a red-shift in their surface plasmon resonance peak from 395 to 580 and 535 nm for Mn2+ and Cd2+ ions, respectively. Moreover, the aggregation of sulfoanthranilic acid dithiocarbamate functionalized silver nanoparticles induced by Mn2+ and Cd2+ ions was confirmed by dynamic light scattering and transmission electron microscopy. The Mn2+ and Cd2+ ion detection method based on their surface plasmon resonance peak using UV-visible spectrophotometry offers wide linear detection ranges from 5 to 50 μM and 10 to 100 μM with detection limits of 1.7 and 5.8 μM for Mn2+ and Cd2+ ions, respectively. The sulfoanthranilic acid dithiocarbamate functionalized silver nanoparticles act as a simple colorimetric probe for the simultaneous detection of Mn2+ and Cd2+ ions in various environmental water samples (drinking, tap, canal and river water) with good recovery values at minimal volumes of samples.

A molecular assembly of piperidine carboxylic acid dithiocarbamate on gold nanoparticles for the selective and sensitive detection of Al3+ ion in water samples

A sensitive and selective colorimetric method has been developed for the detection of Al3+ ions using 4-piperidine carboxylic acid dithiocarbamate-functionalized gold nanoparticles (PCA-DTC-Au NPs) as a probe. A high degree of PCA-DTC-Au NP aggregation was observed following the addition of Al3+ ion in the presence of 0.4 M NaCl in Tris–HCl buffer at pH 6.0. The Al3+ ions effectively induced the aggregation of PCA-DTC-Au NPs, resulting in a color change from red to blue. The characteristic surface plasmon resonance (SPR) peak of PCA-DTC-Au NPs was red-shifted to 660 nm. The Al3+ ion-induced aggregation of PCA-DTC-Au NPs was monitored by UV-visible spectrophotometry. The absorbance ratio (A660 nm/A523 nm) was linear for concentrations of Al3+ ion within the range 0.01–100 μM, with a correlation coefficient of R2 = 0.997. The probe was free from interference due to other metal ions and the color change was extremely specific towards Al3+ ion. The applicability of the present method in practical samples was studied by determining Al3+ ion in spiked water samples (drinking, tap, canal and river water) containing known concentrations of Al3+ ion.

Influence of ligand chemistry on silver nanoparticles for colorimetric detection of Cr 3+ and Hg 2+ ions

In this work, we describe the role of ligand chemistry on the surfaces of silver nanoparticles (Ag NPs) for tuning their analytical applications. The citrate and melamine (MA) molecules were used as ligands for the surface modification of Ag NPs. The addition of Cr3+ ion in citrate-Ag NPs (Cit-Ag NPs) and of Hg2+ ion in melamine-Ag NPs (MA-Ag NPs) cause Ag NPs aggregation, and are accompanied by a color change and a red-shift. The resulting distinctly visual readouts are favorable for colorimetric detection of Cr3+ and Hg2+ ions. Under optimal conditions, the linear ranges are observed in the concentration ranges of 1.0-50.0 and of 10.0-100.0 μM, and with detection limit of 0.52 and 1.80 μM for Cr3+ and Hg2+ ions. The simultaneous detection of Cr3+ and Hg2+ ion is driven by the changing the ligand chemistry on the surfaces of Ag NPs that allows to tune their specific interactions with target analytes. Finally, the functionalized Ag NPs were successfully applied to detect Cr3+ and Hg2+ ions in water samples with satisfactory recoveries.

Recent advances in the direct and nanomaterials-based matrix-assisted laser desorption/ionization mass spectrometric approaches for rapid characterization and identification of foodborne pathogens

In recent years, significant progress has been made in the development of nanomaterials (NMs)-based matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) approaches for rapid detection of foodborne pathogens in food samples. For this reason, a comprehensive literature survey has been carried out aiming to give an overview in the field of foodborne pathogens detection by direct MALDI-MS and NMs-MALDI-MS. New NMs-based MALDI-MS techniques for food pathogen detection are being developed to improve the performance of MALDI-MS with regard to sensitivity and selectivity, which is also rapid, reliable, effective, and suitable for in situ analysis. This chapter presents recent advances in the development of alternative bioanalytical techniques for detection of foodborne pathogens by direct MALDI-MS and NMs-based MALDI-MS in food samples. The role of NMs in pathogen detection by MALDI-MS and their tremendous roles in the development of miniaturized analytical methods for detection of pathogenic bacteria are overviewed. Special attention is paid to methods for improving the analytical parameters of direct and NMs-based MALDI-MS, including sensitivity and analysis time as well as automation of assay procedures. Future directions for NMs-MALDI-MS-based biosensor development and problems related to the commercialization of bacterial biosensors are discussed in the final part of the proposed book chapter.