Digital colorimetric sensor for assessment of iodate in food-grade salt based on paper-based analytical device.

A digital colorimetric sensor was developed for the on-site measurement of iodate in food-grade salt. It involved a paper-based analytical device (PAD) containing an immobilized iodide/starch reagent and a smartphone as the detection system. Iodate ions produce a blue-black coloration on the PAD, the smartphone captures a digital image of the PAD, and an installed mobile app performs an analysis to generate color values related to the intensity of the color in the PAD. Parameters in the image acquisition and PAD preparation were optimized, and a matrix-matched calibration plot was employed for quantification. The plot exhibited a linear response in the concentration range of 10 to 100 mg iodate kg-1 of salt, and a detection limit of 2.20 mg kg-1 was determined. The present method was applied to analyze real samples, and the results agreed well with those obtained using the reference method at the 95% confidence level.

Smartphone-based optical transduction for the rapid microscale assessment of iodate in table salt.

The measurement of iodine in table salt is vital for the successful implementation of the universal salt iodization (USI) program to fight iodine deficiency disorders (IDDs). This paper presents a smartphone-based optical transduction system for iodine measurement in table salt. The method was based on the response in the blue color space generated by the complex formed between the starch/iodide reagent and iodate in the salt sample. The parameters for the color reaction and for the image capture affected the response and were optimized. A matrix effect caused by NaCl was observed and was eliminated through matrix matching by incorporating NaCl in the standard solutions. The optimized method yielded a highly linear response to iodate concentrations ranging from 10 to 160 mg kg-1 (r = 0.9993) with a limit of detection of 2.8 mg kg-1. The method exhibited good accuracy and precision, based on AOAC standards. It produced results that were in agreement with those obtained using the reference method at the 95% confidence level. The smartphone performs optical transduction, as well as signal processing, to yield a display of the iodate concentration in the salt sample. The use of smartphones presents a simple, inexpensive, portable, and widely available device for on-site analysis of iodate in table salt.

Reversible chemiresistive sensing of ultra-low levels of elemental mercury vapor using thermally reduced graphene oxide.

A chemiresistor sensor for ultra-low levels of elemental mercury (Hg0) vapor is described. The sensor was prepared through thermal reduction of graphene oxide (GO) deposited on an interdigitated electrode using only low temperature annealing typically at 230 °C. The sensor responds to the presence of Hg0 vapor within <1 min and spontaneously recovers its baseline through flushing with a Hg0-free carrier gas. The sensor has a linear response in the range of 0.5 to 12.2 ppbv of Hg0 vapor and a detection limit of 0.10 ppbv. The amount of GO and annealing temperature affect the sensor response and were optimized. The sensor can find use in monitoring exposure of persons to Hg0 vapors, for which a threshold value of 6.1 ppbv has been set by the World Health Organization. Graphical abstract Schematic of an interdigitated electrode modified with a layer of thermally reduced graphene oxide. It can be used as a chemiresistive sensor for Hg0 vapor. The sensor displays a rapid and reversible response and has an ultralow detection limit of 0.10 ppbv.

Use of array of conducting polymers for differentiation of coconut oil products.

An array of chemiresistors based on conducting polymers was assembled for the differentiation of coconut oil products. The chemiresistor sensors were fabricated through the potentiostatic electrodeposition of polyaniline (PANi), polypyrrole (PPy) and poly(3-methylthiophene) (P-3MTp) on the gap separating two planar gold electrodes set on a Teflon substrate. The change in electrical resistance of the sensors was measured and observed after exposing the array to the headspace of oil samples. The sensor response was found rapid, reversible and reproducible. Different signals were obtained for each coconut oil sample and pattern recognition techniques were employed for the analysis of the data. The developed system was able to distinguish virgin coconut oil (VCO) from refined, bleached & deodorised coconut oil (RBDCO), flavoured VCO, homemade VCO, and rancid VCO.

Biomimetic piezoelectric quartz crystal sensor with chloramphenicol-imprinted polymer sensing layer.

The measurement of banned antibiotic like chloramphenicol is significant for customer protection and safety. The presence of residual antibiotics in foods and food products of animal origin could pose as health hazards and affect food quality for global acceptance. In this study, the potential of a chloramphenicol sensor based on molecularly imprinted polymer (MIP) coupled with a piezoelectric quartz crystal was explored. The MIP was prepared by precipitation polymerization at 60 °C. Methacrylic acid was used as monomer, trimethylolpropane trimethacrylate (TRIM) as crosslinker, and chloramphenicol as the template. Template removal on the resulting polymer was done by extraction using methanol-acetic acid. Characterization of the MIP and NIP were conducted by spectroscopic and microscopic methods. These further supported the imprinting and rebinding process of chloramphenicol to the polymer matrix. The chloramphenicol sensor was devised by spin-coating onto one side of the 10 MHz AT-cut quartz crystal the MIP suspension in polyvinylchloride-tetrahydrofuran (6:2:1 w/w/v) solution. Optimization of sensor response was performed by varying the type of cross-linker, amount of MIP sensing layer, curing time, and pH. The sensor exhibited good sensitivity of about 73 Hz/log (conc., µg mL(-1)) and good repeatability (rsd<10%). A linear relationship (r(2)=0.9901) between frequency shift and chloramphenicol concentration in the range of 1×10(-6) up to 1×10(-1) µg/mL was obtained. The sensor response was highly selective to chloramphenicol than with other compounds of similar chemical structures. Acceptable percent recovery was obtained for real sample analysis using the sensor. The proposed sensor could be a promising low cost and highly sensitive approach for residual chloramphenicol quantification in food products.

Enantioselective piezoelectric quartz crystal sensor for d-methamphetamine based on a molecularly imprinted polymer.

A piezoelectric quartz crystal (PQC) sensor based on a molecularly imprinted polymer (MIP) has been developed for enantioselective and quantitative analysis of d-(+)-methamphetamine (d(+)-MA). The sensor was produced by bulk polymerization and the resulting MIP was then coated on the gold electrode of an AT-cut quartz crystal. Conditions such as volume of polymer coating, curing time, type of PQC, baseline solvent, pH, and buffer type were found to affect the sensor response and were therefore optimized. The PQC-MIP gave a stable response to different concentrations of d(+)-MA standard solutions (response time = 10 to 100 s) with good repeatability (RSD = 0.03 to 3.09%; n = 3), good reproducibility (RSD = 3.55%; n = 5), and good reversibility (RSD = 0.36%; n = 3). The linear range of the sensor covered five orders of magnitude of analyte concentration, ranging from 10(-5) to 10(-1) microg mL(-1), and the limit of detection was calculated as 11.9 pg d(+)-MA mL(-1) . The sensor had a highly enantioselective response to d(+)-MA compared with its response to l(-)-MA, racemic MA, and phentermine. The developed sensor was validated by applying it to human urine samples from drug-free individuals spiked with standard d(+)-MA and from a confirmed MA user. Use of the standard addition method (SAM) and samples spiked with d(+)-MA at levels ranging from 1 x 10(-3) to 1 x 10(-2) microg mL(-1) showed recovery was good (95.3 to 110.9%).