A Novel Fluorescent and Colorimetric Method for the Determination of Formaldehyde Based on Albumin Nanoparticles-Polyethyleneimine-Ag+ Ion Nanohybrids

As a carcinogenic substance, high dose of formaldehyde exposure may lead to poisoning and even death. Long-term exposure to low doses of formaldehyde can harm human skin, respiratory organs and immune system. Therefore, it is vital to detect formaldehyde content in real time. In this paper, a simple method for the determination of formaldehyde based on fluorometry and colorimetry was established in the range of 0-1.92 mg·mL-1. A fluorescence protein nanoparticles (BSA NPs) was prepared utlizing bovine serum albumin (BSA) as the raw material. Based on the silver mirror reaction, silver nanoparticles can be generated from the reaction between BSA NPs combined with polyethylenimide (PEI) and silver ion (Ag+) ions complex (BSA NPs-PEI-Ag) and formaldehyde. The fluorescent detection principle for formaldehyde was based on the fluorescence queching of BSA NPs-PEI-Ag system at 514 nm upon the reduction of Ag+ ions by formaldehyde. The colorimetric detection principle for formaldehyde was based on the enhancement of absorption band of BSA NPs-PEI-Ag system at 460 nm and color changes along with the generation of silver nanoparticles after the addition of formaldehyde. The proposed method was succesfully used for formaldehyde detection in real water sample with the recovery range of 106-110%.

RGB color analysis of formaldehyde in vegetables based on DNA functionalized gold nanoparticles and triplex DNA

A highly sensitive and selective RGB color analysis for the detection of formaldehyde (FA) was developed by using a DNA functionalized gold nanoparticle (AuNPs-DNA) probe. When complementary oligonucleotides (oligo 2 and oligo 3) and a silver ion (Ag⁺) were added to the AuNPs-DNA solution, triplex DNA was formed, resulting in the aggregation of AuNPs, and accompanied by a solution color change from red to purple. With the addition of formaldehyde, it reacted with Ag⁺, decreased the stability of triplex DNA between AuNPs-DNA, induced the dispersion of AuNPs, and the color of AuNPs recovered to red. Therefore, the formaldehyde concentration could be estimated with the RGB (red, green, blue) values of the AuNP solution by using a smartphone application (APP). The R value of the system was proportional to the concentration of formaldehyde within the range of 0.23-4.50 mg L^-1, with a detection limit of 0.14 mg L^-1. The method has been successfully applied to detect the residues of formaldehyde in vegetable samples and has the potential of the on-site determination of formaldehyde.

A novel colorimetric sensor array for real-time and on-site monitoring of meat freshness

Food quality control is essential in industry and daily life. In this work, we developed a novel colorimetric sensor array composed of several pH-sensitive dyes for monitoring meat freshness. A color change in the sensor array was seen after exposure to volatile organic compounds (VOCs), and the images were captured for precise quantification of the VOCs. In conjunction with pattern recognition, meat freshness at different storage periods was readily discerned, revealing that the as-fabricated colorimetric sensor array possessed excellent discrimination ability. The linear range for quantitative analysis of volatiles related to meat spoilage was from 5 ppm to 100 ppm, with a limit of detection at the ppb level (S/N = 3). Furthermore, the testing results obtained by the sensor in assessing meat freshness were validated by a standard method for measuring the total volatile basic nitrogen (TVB-N). The sensing signals showed good agreement with the results obtained in TVB-N when measuring real food samples. The sensor also displayed good reproducibility (RSD < 5%) and long-term stability. The sensor was successfully used for on-site and real-time determination of volatiles emitted from rotting meat, demonstrating its potential application in monitoring the quality and safety of meat products.

Toward ultrasensitive and fast colorimetric detection of indoor formaldehyde across the visible region using cetyltrimethylammonium chloride-capped bone-shaped gold nanorods as “chromophores”

A colorimetric method for detecting formaldehyde was developed by coupling bone-shaped gold nanorods (AuNRs) with silver mirror reaction, which enables low detection limit, wide linear range and high visual resolution.

Determination of Formaldehyde by HPLC with Stable Precolumn Derivatization in Egyptian Dairy Products

Formaldehyde is one of the most dangerous chemical compounds affecting the human health; exposure to it from food may occur naturally or by intentional addition. In this study a high performance liquid chromatography method for determination of formaldehyde in dairy products was described. The dairy samples were reacted and extracted with a warmed organic solvent in the presence of derivatizing agent 2,4-dinitrophenylhydrazine (DNPH) and formaldehyde; the mixture was centrifuged and followed by diode array detection. The method is validated and gives average recovery of formaldehyde at the three different levels 0.1, 5.0, and 10.0 mg/kg varied between 89% and 96%. The method is linear from the limit of quantification 0.1 mg/kg up to 10 mg/kg levels. This method is intended for formaldehyde analyses in dairy products simply with stable derivatization, minimum residue loss, excellent recovery, and accurate results with a sensitive limit of detection 0.01 mg/kg. 90 dairy samples from milk, cheese, and yogurt were investigated from seven Egyptian governorates and all samples were free from formaldehyde.

Selectivity/Specificity Improvement Strategies in Surface-Enhanced Raman Spectroscopy Analysis

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for the discrimination, identification, and potential quantification of certain compounds/organisms. However, its real application is challenging due to the multiple interference from the complicated detection matrix. Therefore, selective/specific detection is crucial for the real application of SERS technique. We summarize in this review five selective/specific detection techniques (chemical reaction, antibody, aptamer, molecularly imprinted polymers and microfluidics), which can be applied for the rapid and reliable selective/specific detection when coupled with SERS technique.

A “turn-off” fluorescent sensor for the selective and sensitive detection of copper(ii) ions using lysozyme stabilized gold nanoclusters

In this contribution, we have developed a simple, environmentally friendly fluorescent turn-off sensor for the detection of copper (Cu²⁺) ions in aqueous solution by using lysozyme stabilized gold nanoclusters (Lys-AuNCs) as a fluorescent probe.