A step towards mobile arsenic measurement for surface waters

High sensitivity atomic fluorescence spectroscopy for the detection of AsIII by selective electrolysis of arsenic on nanoflowers-like Fe/NFE

Modified electrosynthetic sample introduction technique is a reliable means of solving the problem of high sensitivity analysis of trace arsenite. This article attempts to achieve selective electroreduction of AsIII through the construction of electrode surfaces with different structures and materials from the perspective of interface reactions. Among the four transition metal modifiers, the iron modified nickel foam electrode with nano-flower structure documented higher efficiency in inducing arsenic reduction and better species selectivity. Systematic electrochemical and spectroscopic tests suggest that strong adsorption effect between Fe and AsIII, appropriate hydrogen evolution potential, and catalytic activity jointly promote efficient electroreduction of AsIII. Optimization based on electrode materials and electrolysis conditions, with high sensitivity, wide linear range (0.1-50 μg L-1), and excellent species selectivity, this paper offers an efficient and economic sample introduction method for trace AsIII/V selective atomic spectroscopy direct determination.

Coordination polymer gel mediated spectrophotometric, ICP-AES and spectrofluorimetric methods for trace As(III) determination in water and food samples

Herein, a coordination polymer gel is proposed for the determination of As(III) in real samples through multispectroscopic techniques viz. spectrophotometry, spectrofluorimetry, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Taguchi L32 (46 21) design and adaptive neuro fuzzy inference system (ANFIS) optimized the controllable factors affecting the extraction yielding an experimental S/N ratio of 39.94 dB. The fluorescence quenching (KSV = 2.63 × 106 L mol-1) was static with photoelectron transfer being the main mechanism confirmed by the density functional theory calculations. The limits of detection (LODs), limits of quantification (LOQs) and linear ranges were 0.038 μg L-1, 0.13 μg L-1 and 1.67-116.67 μg L-1, 0.40 μg L-1, 1.21 μg L-1 and 1.67-33.33 μg L-1, 1.07 μg L-1, 3.24 μg L-1 and 3.32-35.37 μg L-1 for the developed enrichment coupled ICP-AES, spectrophotometry and fluorescence sensing methods. Among these methods, the enrichment - ICP-AES method has the lowest LOD, LOQ and the widest linear range followed by the enrichment - spectrophotometry and fluorescene sensing methods. Spectrofluorimetry offers high sensitivity, selectivity, and possible real time monitoring, spectrophotometry provides a cost-effective and versatile option, while ICP-AES manifests multi-element analysis with high sensitivity and low interference. The developed methods were validated and employed for the successful determination of trace As(III) in real samples. The employment of these methods enhances the overall analytical capability for a wide range of sample types and concentrations.

L-cysteine functionalized graphene quantum dots for sub-ppb detection of As (III)

Here, we report functionalized graphene quantum dots (GQDs) for the optical detection of arsenic at room temperature. GQDs with the fluorescence of three fundamental colors (red, green, and blue) were synthesized and functionally capped with L-cysteine (L-cys) to impart selectively towards As (III) by exploiting the affinity of L-cys towards arsenite. The optical characterization of GQDs was carried out using UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy, and fluorescence spectrometry, and the structural characterizations were performed using transmission electron microscopy. The fluorescence results showed instantaneous quenching in intensity when the GQDs came in contact with As (III) for all test concentrations over a range from 0.025 to 25 ppb, which covers the permissible limit of arsenic in drinking water. The experimental results suggested excellent sensitivity and selectivity towards As (III).

Smartphone-based optical analysis systems

During the past few decades, there has been a growing trend towards the use of smartphone-based analysis systems. This is mainly due to its ubiquity, its increasing computing capacity, its relatively low cost and the ability to acquire and process data at the same time. Furthermore, there are many sensors integrated into a smartphone, for example a complementary metal-oxide semiconductor (CMOS) sensor. A CMOS sensor enables optical analysis for example by using it as a colorimeter, photometer or spectrometer. This review explores the current state-of-the-art smartphone-based optical analysis systems in various areas of application. It is organized into three sections, each of which investigates one class of smartphone-based devices: (i) smartphone-based colorimeters (ii) smartphone-based photo- and spectrometers and (iii) smartphone-based fluorimeters.

Self-plasticized, lumogallion-based fluorescent optical sensor for the determination of aluminium (III) with ultra-low detection limits

Aluminium-selective ion optical sensor based on covalently attached lumogallion methacrylate was synthesized and investigated in this study. Lumogallion based derivatives were copolymerized with various methacrylate monomers via a simple one step free radical polymerization to produce a "self-plasticized" copolymer. We demonstrate that covalently attached lumogallion moieties provide adequate functionality to the optical film thus achieving a very simple, one component sensing membrane. Fluorescence experiments demonstrated excellent sensitivity towards aluminium (III) ions with the detection limits found at 4.8 × 10^-12 M. Furthermore, proposed sensor displays high selectivity towards aluminium over a number of biologically relevant cations. Moreover, the synthesized copolymer was used for the fabrication of nanoparticles that exhibit strong fluorescence upon contact with aluminium (III) ions. It is anticipated that lumogallion-based copolymers may form the basis for the development of highly sensitive and robust aluminium selective sensors capable of in situ measurements.

Development of ultrasensitive and As(iii)-selective upconverting (NaYF4:Yb3+,Er3+) platform

Solid-phase, LRET-based NaYF₄:Yb³⁺,Er³⁺ platform for the ultrasensitive (1 nM) detection of arsenic.

Arsenic sensor development based on modification with (E)-N′-(2-nitrobenzylidine)-benzenesulfonohydrazide: a real sample analysis

(E)-N′-(2-Nitrobenzylidene)-benzenesulfonohydrazide was prepared from 2-nitrobenzaldehyde and benzenesulfonylhydrazine by using a condensation method and applied as a selective As³⁺ sensor.

Time-resolved and temperature tuneable measurements of fluorescent intensity using a smartphone fluorimeter

A smartphone fluorimeter capable of time-based fluorescence intensity measurements at various temperatures is reported. Excitation is provided by an integrated UV LED (λ_ex = 370 nm) and detection obtained using the in-built CMOS camera. A Peltier is integrated to allow measurements of the intensity over T = 10 to 40 °C. All components are controlled using a smartphone battery powered Arduino microcontroller and a customised Android application that allows sequential fluorescence imaging and quantification every δt = 4 seconds. The temperature dependence of fluorescence intensity for four emitters (rhodamine B, rhodamine 6G, 5,10,15,20-tetraphenylporphyrin and 6-(1,4,8,11-tetraazacyclotetradecane)2-ethyl-naphthalimide) are characterised. The normalised fluorescence intensity over time of the latter chemosensor dye complex in the presence of Zn²⁺ is observed to accelerate with an increasing rate constant, k = 1.94 min^-1 at T = 15 °C and k = 3.64 min^-1 at T = 30 °C, approaching a factor of ∼2 with only a change in temperature of ΔT = 15 °C. Thermally tuning these twist and bend associated rates to optimise sensor approaches and device applications is proposed.

Surface Modifications of Nanoparticles for Stability in Biological Fluids

Due to the high surface: volume ratio and the extraordinary properties arising from the nanoscale (optical, electric, magnetic, etc.), nanoparticles (NPs) are excellent candidates for multiple applications. In this context, nanoscience is opening a wide range of modern technologies in biological and biomedical fields, among others. However, one of the main drawbacks that still delays its fast evolution and effectiveness is related to the behavior of nanomaterials in the presence of biological fluids. Unfortunately, biological fluids are characterized by high ionic strengths which usually induce NP aggregation. Besides this problem, the high content in biomacromolecules—such as lipids, sugars, nucleic acids and, especially, proteins—also affects NP stability and its viability for some applications due to, for example, the formation of the protein corona around the NPs. Here, we will review the most common strategies to achieve stable NPs dispersions in high ionic strength fluids and, also, antifouling strategies to avoid the protein adsorption.

Thermally stable hybrid polyarylidene(azomethine-ether)s polymers (PAAP): an ultrasensitive arsenic(III) sensor approach

A new category of thermally stable hybrid polyarylidene(azomethine-ether)s and copolyarylidene(azomethine-ether)s (PAAP) based on diarylidenecycloalkanones has been synthesized using solution polycondensation method. For potential cationic sensor development, a thin layer of PAAP onto a flat glassy carbon electrode (GCE, surface area: 0.0316 cm²) was prepared with conducting nafion (5%) coating agent to fabricate a sensitive and selective arsenic (III) [As³⁺] ion in short response time in neutral buffer system. The fabricated cationic sensor was measured the analytical performances such as higher sensitivity, linear dynamic range, detection limit, reproducibility, and long-term stability towards As³⁺ ions. The sensitivity and detection limit were calculated as 2.714 μAμM^-1cm^-2 and 6.8 ± 0.1 nM (SNR of 3; 3N/S) respectively from the calibration curve. This novel approach can be initiated a well-organized route of an efficient development of heavy selective arsenic sensor for hazardous pollutants in biological, environmental, and health care fields. Real sample analysis for various environmental sample was performed with PAAP-modified-GCE.

A "Turn-On" thiol functionalized fluorescent carbon quantum dot based chemosensory system for arsenite detection

Carbon quantum dots (CQDs) have emerged out as promising fluorescent probes for hazardous heavy metals detection in recent past. In this study, water soluble CQDs were synthesized by facile microwave pyrolysis of citric acid & cysteamine, and functionalized with ditheritheritol to impart thiol functionalities at surface for selective detection of toxic arsenite in water. Microscopic analysis reveals that the synthesized CQDs are of uniform size (diameter ∼5nm) and confirmed to have surface SH groups by FT-IR. The functionalized probe is then demonstrated for arsenite detection in water by "Turn-On" read out mechanism, which reduces the possibility of false positive signals associated with "turn off' probes reported earlier. The blue luminescent functionalized CQDs exhibit increase in fluorescence intensity on arsenite addition in 5-100ppb wide detection range. The probe can be used for sensitive detection of arsenite in environmental water to a theoretical detection limit (3s) of 0.086ppb (R²=0.9547) with good reproducibility at 2.6% relative standard deviation. The presented reliable, sensitive, rapid fCQDs probe demonstrated to exhibit high selectivity towards arsenite and exemplified for real water samples as well. The analytical performance of the presented probe is comparable to existing organic & semiconductor based optical probes.