Rapid and Highly Selective Detection of Heavy Metal Ions in Drinking Water using Nanosensor Based Colorimetric Assay

Owing to excessive usage, over time, heavy metal ions have brought on serious environmental issues as well as health hazards in living systems. Sources of drinking watergetting contaminated by heavy metals is one of the most prominent concerns among these. Hence, constructing an accurate method for the determination of heavy metals in water bodies is of great importance. In the current context, several quantitative techniques like atomic absorption spectrometry, high-performance liquid chromatography and chemiluminescence are available for this purpose. However, these methods have certain drawbacks such as long assay time, high cost and the need of sophisticated instruments and well-trained personnel. Therefore, the development of a simple, cost effective and efficient method for the detection of heavy metal ions is desirable in order to delimit its harmful effects. This study is conducted with the aim of developing a nanosensor to account for this cause. Out of various nanomaterials used in sensing applications, silver nanoparticles (AgNPs) are particularly outstanding as they possess unique optical performance. AgNPs were synthesised by reduction of silver nitrate using hydroxylamine hydrochloride. Synthesized AgNPs were then surface functionalised with two distinct ligands on two separate occasions, namely, L-cysteine and 4-mercaptobenzoic acid (4-MBA). Both these ligands contain a thiol group which displays high affinity for Ag surfaces and a carboxyl group which can interact with the surrounding, or in this case, to act as a sensor formetal ions. These nanoprobes were tested against standards of various metal ions. The presence of Cd2+ induces the aggregation of L-cysteine functionalised AgNPs whereas 4-MBA functionalised AgNPs undergo aggregation in the presence of Cr3+ ions. In both these instances, AgNPs get linked together by “carboxylate-metal ion-carboxylate” coordinative couplings, resulting in a colour change from yellow to deep orange. The concentration of the respective metal ion in each case could be monitored by the colorimetric response obtained by UV-Vis spectroscopy or even naked eyes and the detection limit is as low as 1 ppm. This novel detection system could be successfully applied to determine Cd2+ and Cr3+in drinking water.Keywords: Silver nanoparticles, Cadmium ions, Chromium ions, Nanosensor, Colorimetr

Fluorescence spectroscopy characterization of turbine oil (Caltex Regal R&O 68) used in Samanala Dam hydropower plant in Sri Lanka

The energy crisis is a major issue not only in Sri Lanka but also globally. One of the major issues pertaining to this crisis is the extant use of nonrenewable sources such as oil, coal and natural gas. Hydro power is a major renewable energy source that can be used to generate the electricity requirements of Sri Lanka. It is necessary for a hydropower turbine to function efficiently without any failures to generate electricity. The lubricants used in gearboxes of turbines play a major role in the proper functioning of hydropower turbines. Here, researchers have studied spectroscopic differences of new and discarded Caltex Regal R & O 68 using Raman spectroscopy, Fourier Transform InfraRed (FTIR) spectroscopy and fluorescence spectroscopy. Among spectra obtained from above spectroscopic techniques, the spectra obtained from fluorescence spectroscopy had a significant difference between two lubricant samples. The highest fluorescence intensity was recorded in the fresh/ new oil sample while the lowest intensity was in the oil which was discarded by the hydro turbines. Additionally, in this study, it was revealed how fluorescence intensity of turbine oil (Caltex Regal R&O 68) used in Samanala hydropower plant station varies with different temperatures 100 °C, 120 °C, 140 °C, and 200 °C. Moreover, 1-Naphthalenamine, N – phenyl was identified as the fluorophore used in Caltex Regal R&O 68 lubricant. Therefore, the fluorescence technique can be used as a tool for monitoring the quality of  hydropower turbine oils. KEYWORDS: Oil degradation, Antioxidants, Fluorescence intensity, Renewable energy, Fluorophor

Intracellular multiplex detection and imaging of stable chemisorbed labels by SERS spectroscopy

SERS spectroscopy is currently gaining wider acceptance in biological research due to its ability to obtain signals from very low quantities of material, and to obtain information from within live cells. SERS spectroscopy yields very narrow bands (10-100 times narrower than typical fluorescence bands) and spectra suffer from minimal interference from aqueous media, making SERS spectroscopy ideal for multiplex detection of intracellular components. Typically for sensing, nanoparticles are labelled with suitable sensing molecules such as a dye or thiol. Nanoparticle labelling involves two different types of interaction between the label and the enhancing surface, chemisorption and physisorption. The former is considerably stronger and more stable than the latter and hence chemisorbed labels are more appropriate for intracellular nanosensor design. In this paper, we demonstrate the difference in stability of both types of Raman label inside live cells over periods of time. Chinese hamster ovary (CHO) cells were infused with a mixture of differently labelled stable nanosensors and were imaged using SERS microspectroscopy. We also demonstrate the applicability of SERS mapping for high-throughput multiplex detection using micropatterned cell arrays

Monitoring the uptake and redistribution of metal nanoparticles during cell culture using surface-enhanced raman scattering spectroscopy

We describe the uptake of silver nanoparticles by CHO (Chinese hamster ovary) cells and their subsequent fate as a result of cell division during culture, as monitored by surface-enhanced Raman scattering (SERS) spectroscopy. Mapping of populations of cells containing both labeled and native nanoparticles by SERS spectroscopy imaging provided a quantitative method by which the number of intracellular nanoparticles could be monitored. Initially, for a given amount of nanoparticles, the relationship between the number taken up into the cell and the time of incubation was explored. Subsequently, the redistribution of intracellular nanoparticles upon multiple rounds of cell division was investigated. Intracellular SERS signatures remained detectable in the cells for up to four generations, although the abundance and intensity of the signals declined rapidly as nanoparticles were shared with daughter cells. The intensity of the SERS signal was dependent both on stability of the label and their abundance (nanoparticle aggregation increases the extent of the SERS enhancement). The data show that while the labeled nanoparticles remain stable for prolonged periods, during cell division, the changes in signal could be attributed both to a decrease in abundance and distribution (and hence aggregation

SERS mapping of nanoparticle labels in single cells using a microfluidic chip

We report for the first time the time-resolved mapping of intracellular nanoparticle labels from within living cells retained in a microstructured trap using Raman spectroscopy. The methods employed here also demonstrate the ability to rapidly discriminate between cell populations containing different SERS labels

Development of sampling methods for Raman analysis of solid dosage forms of therapeutic and illicit drugs

The results of a study aimed at determining the most important experimental parameters for automated, quantitative analysis of solid dosage form pharmaceuticals (seized and model 'ecstasy' tablets) are reported. Data obtained with a macro‐Raman spectrometer were complemented by micro‐Raman measurements, which gave information on particle size and provided excellent data for developing statistical models of the sampling errors associated with collecting data as a series of grid points on the tablets' surface. Spectra recorded at single points on the surface of seized MDMA-caffeine-lactose tablets with a Raman microscope (λex = 785 nm, 3 µm diameter spot) were typically dominated by one or other of the three components, consistent with Raman mapping data which showed the drug and caffeine microcrystals were ca 40 µm in diameter. Spectra collected with a microscope from eight points on a 200 µm grid were combined and in the resultant spectra the average value of the Raman band intensity ratio used to quantify the MDMA: caffeine ratio, µr, was 1.19 with an unacceptably high standard deviation, σr, of 1.20. In contrast, with a conventional macro‐Raman system (150 µm spot diameter), combined eight grid point data gave µr = 1.47 with σr = 0.16. A simple statistical model which could be used to predict σr under the various conditions used was developed. The model showed that the decrease in σr on moving to a 150 µm spot was too large to be due entirely to the increased spot diameter but was consistent with the increased sampling volume that arose from a combination of the larger spot size and depth of focus in the macroscopic system. With the macro‐Raman system, combining 64 grid points (0.5 mm spacing and 1-2 s accumulation per point) to give a single averaged spectrum for a tablet was found to be a practical balance between minimizing sampling errors and keeping overhead times at an acceptable level. The effectiveness of this sampling strategy was also tested by quantitative analysis of a set of model ecstasy tablets prepared from MDEA-sorbitol (0-30% by mass MDEA). A simple univariate calibration model of averaged 64 point data had R2 = 0.998 and an r.m.s. standard error of prediction of 1.1% whereas data obtained by sampling just four points on the same tablet showed deviations from the calibration of up to 5%