Colorimetric detection of iron (II) using 4-mercaptobenzoic acid and 3,3′,5,5′-tetramethylbenzidine modified silver nanoparticles

Anti-aggregation colorimetric sensing of cysteine using silver nanoparticles in the presence of Pb2

Using silver nitrate as the silver source and sodium borohydride as the reducing agent, we synthesized negatively charged silver nanoparticles (AgNPs). Subsequently, the AgNPs solution was mixed with positively charged lead ions, resulting in AgNPs aggregation via electrostatic interactions. This led to a color change in the solution from yellow to purple and eventually to blue-green. Our study focused on a colorimetric method that exhibited high selectivity and sensitivity in detecting cysteine using AgNPs-Pb2+ as a sensing probe. Upon the introduction of cysteine to the AgNPs-Pb2+ system, the absorbance of AgNPs increased at 396 nm and decreased at 520 nm. The formation of a complex between cysteine and lead ions prevented the aggregation of silver nanoparticles, enabling the colorimetric detection of cysteine. The relationship between the concentration of ΔA396/A520 and cysteine showed linearity within the range of 0.01 to 0.1 μM; the regression equation of the calibration curve is ΔA396/A520 = 9.0005c - 0.0557 (c: μM), with an R2 value of 0.9997. The detection limit was found to be 3.8 nM (S/N = 3). This method demonstrated exceptional selectivity and sensitivity for cysteine and was effectively used for the determination of cysteine in urine. Our findings offer a new perspective for the future advancement of anti-aggregation silver nanocolorimetry.

Microflow injection analysis based on modular 3D platforms and colorimetric detection for Fe(III) monitoring in a wide concentration range

A modular microflow injection analysis (microFIA) system for the determination of Fe(III) in a bioleaching reactor has been designed, developed and validated. The different modules of the analyzer (mixer, diluter, disperser and detector) were 3D-printed. Fe(III) quantification is due by measuring the color intensity of the chelate formed between Fe(III) and salicylic acid at 525 nm. The device has been designed to dilute, disperse and detect high Fe(III) concentrations in the form of an inexpensive multi-step photometric flow cell that uses an light-emitting diode (LED) as a light source and an light-dependent resistor (LDR) as a light intensity detector. This microFIA system has been shown to be suitable for automatic and continuous determination of Fe(III) in the operation of a bioreactor for the oxidation of Fe(II). The device has a good repeatability (less than 5% of coefficient of variation in the whole range of concentrations) and accuracy of around 100%. The analyzer features an exceptional wide linear range, between 25 and 6000 mg·L-1. The device was successfully applied to the determination of Fe(III) in real samples. The obtained results proved that the method is applicable for accurate, precise, rapid, and low-cost colorimetric analysis and didn't show significant differences with a conventional UV-Vis method.

A Novel Polymer Inclusion Membrane-Based Green Optical Sensor for Selective Determination of Iron: Design, Characterization, and Analytical Applications

The design, characterization, and analytical application of a green optical sensor for the selective determination of Fe(II) ions is proposed. The sensor is based on the immobilization of the chromogenic reagent picolinaldehyde salicyloylhydrazone (SHPA) within a polymer inclusion membrane. To reduce solvent usage, the reagent was synthesized using a green mechanochemical procedure. The components for sensor preparation were optimized with a sequential simplex method and the optimal composition was found to be 0.59 g cellulose triacetate (base polymer), 0.04 g SHPA (chemosensor reagent), 4.9 mL dibutyl phthalate (plasticizer), and 38 mL dichloromethane (solvent). The conditions of iron analysis were also optimized resulting in pH 6 for aqueous solution, 90 min exposure time and 10 min short-term stability. The optical sensor showed a linear range from the limit of detection (0.48 µmol L-1) to 54 µmol L-1 Fe(II). The precision of the method was found to be 1.44% and 1.19% for 17.9 and 45 µmol L-1 Fe(II), respectively. The characteristics of the sensor allowed the design of a Fe(II)/Fe(III) speciation scheme. The methodology was successfully applied to the determination of iron in food preservatives, food additives, and dietary supplement. Additionally, the Fe speciation scheme was successfully applied to an agricultural fertilizer.

Discriminating detection of dissolved ferrous and ferric ions using copper nanocluster-based fluorescent probe

Discrimination and detection of specific metal ions that belong to the same metallic element with different valence states in a complex matrix is challenging. In the present work, a fluorescence method using polyvinylpyrrolidone stabilized copper nanocluster (CuNCs@PVP) as a probe for discriminating detection of ferrous (Fe³⁺) and ferric (Fe²⁺) ions was developed. The CuNCs@PVP exhibited an excellent selective response to Fe³⁺ ions in contrast to Fe²⁺ ions and other metal ions when the pH value of solution was less than 4.0. Furthermore, the fluorescence of the CuNCs@PVP could be more sensitively quenched by Fe²⁺ ions by virtue of Fenton reaction. The different response of CuNCs@PVP towards Fe³⁺ and Fe²⁺ ions under different conditions offered the potential for the discriminating detection of Fe³⁺ and Fe²⁺ ions. Based on detailed optimization of detection conditions, an excellent linear relationship between the fluorescence quenching efficiency (F/F₀) of the CuNCs@PVP and the concentration of Fe³⁺ ions over the range of 0.4-20.0 μM and of Fe²⁺ ions in the range of 0.01-0.4 μM were obtained, respectively. The detection limits for the Fe³⁺ and Fe²⁺ ions were 0.14 μM and 0.008 μM, respectively. The developed probe showed good selectivity and presented an alternative strategy for discriminating detection of Fe³⁺ and Fe²⁺ ions in complex samples.