Abstract
Hypochlorite plays a critical role in killing microorganisms in the water. However, it can also cause cardiovascular diseases, neuron degeneration, and cancer to humans. Although traditional methods feature excellent sensitivity and reliability in detecting hypochlorite, the expensive instruments and strict determination conditions have limited their application in environmental analysis to some extent. Thus, it is necessary and urgent to propose a cheap, facile, and quick analytical assay for hypochlorite. This paper proposes a colorimetric assay for hypochlorite utilizing gold nanorods (AuNRs) as the nanoreactor and color reader. The AuNRs were acquired via a reported seed-mediated method. NaClO with strong oxidation property can cause the etching of gold from the longitudinal tips of AuNRs, which could shorten the aspect ratio of AuNRs, decrease the absorption in the UV–Vis spectrum and also induce the solution color changing from red to pale yellow. Thus, according to the solution color change and the absorbance of longitudinal surface plasmon resonance of AuNRs, we established the calibration curve of NaClO within 0.08 μM to 125 μM (∆Abs = 0.0547 + 0.004 CNaClO, R2 = 0.9631). Compared to traditional method, we obtained the conversion formula between the concentration of residual-chlorine in tap water and the concentration of hypochlorite detected by the proposed colorimetric assay, which is Cresidual-chlorine = 0.24 CNaClO. Finally, the real application of the colorimetric assay in tap water was successfully performed, and the accuracy of the colorimetric method can reach from −6.78% to +8.53%.
Highlights
In the human immune system, hypochlorite is famous for its special antibacterial properties [1,2].Chlorination disinfection has been added legally and illegally in water treatment, household bleach, and beverage industries [3,4,5]
Hypochlorite (HClO) and sodium hypochlorite (NaClO) have already been presented in drinking water, beverages, infant formula and raw meat in the range of 10−5 M to 10−2 M, which largely threats the health of humans [7]
HClO and NaClO, including gas chromatography-flame ionization detection (GC-FID), fluorescence technique based on gold nanoclusters or organic probe, multi-syringe flow injection analysis system, and electrochemical methods [7,9,10,11,12,13,14]
Summary
In the human immune system, hypochlorite is famous for its special antibacterial properties [1,2]. It is emergent to establish an easy, inexpensive, and quick analytical methods for hypochlorite in water quality and food safety Metallic nanoparticles, such as gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), have acquired great concern due to their unique distance-, size- and shape-dependent physical properties, and show enormous applications in the field of colorimetric assay. There have been colorimetric sensors for metal ions [27,28], I− [29], acetylcholinesterase [30], and small molecules [31,32,33,34], based on the oxidative etching of gold nanoparticles. Based on the simple and sensitive colorimetric method, we achieved the detection of residual chlorine in fresh tap water, which showed great potential promise in environmental application field
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