Rapidly colorimetric detection of caffeine in beverages by silver nanoparticle sensors coupled with magnetic molecularly imprinted polymeric microspheres

Abstract

Excessively intaking caffeine can harm human health, and it is imperative to develop a rapid method to identify caffeine for food safety. The magnetic molecularly imprinted polymeric microspheres (MMIPs) were prepared to pretreat samples before silver nanoparticles (AgNPs) colorimetric detection of caffeine.Using Fe 3 O 4 as supporting core, mesoporous SiO 2 as intermediate shell, a-methylacrylic acid as functional monomer and caffeine as template, the prepared MMIPs were characterised by transmission electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometer. Adsorption process followed Langmuir adsorption isotherm with maximum adsorption capacity at 38.8 mg g À1 under 298 K. The MMIPs extract caffeine from beverages, then the AgNPs colorimetric method rapidly screened and semi-quantified caffeine ≥5 mg L À1 by naked eye, and accurately quantified caffeine ranging 0.1-5 mg L À1 by UV-vis spectroscopy at 393 nm, which were consistent with HPLC analytical results. Thus, this method might be used to rapidly enrich and analyse caffeine in beverages.

Vinyl Phosphate-Functionalized, Magnetic, Molecularly-Imprinted Polymeric Microspheres’ Enrichment and Carbon Dots’ Fluorescence-Detection of Organophosphorus Pesticide Residues

“…The adsorption capacity increased with the increase of temperature; perhaps the reason was that the MMIPs could be swollen easily under higher temperature so that more binding sites were exposed. Thus, the adsorption capacity at a higher temperature was greater than that at low temperature, which is consistent with the results of relevant literature [28,30,40].…”

“…According to the correlation coefficient (R 2 ) shown in Table S2 (in Supporting Materials), the adsorption of triazophos on the dual functional monomers MMIPs and MINPs conformed to a pseudo-second-order kinetics model because the R 2 values of both were higher than 0.98. The calculated equilibrium adsorption value (0.160 mmol g −1 ) of MMIPs was close to the actual equilibrium adsorption value (0.167 mmol g −1 ) at 308 K. The results indicated that both external diffusion and intraparticle diffusion existed simultaneously [30].…”

“…In the molecularly-imprinted surface polymerization reaction, triazophos (0.25 mmol) and the four functional monomers MAA, 4-VP, VPA, and 1-Oc (0.25 mmol) were dissolved in methanol (12.0 mL), respectively, purged with N 2 , and then stored in a refrigerator at 4 °C for 12 h to prepare a preassembled solution. Vinyl-modified Fe 3 O 4 @mSiO 2 (50.0 mg), EGDMA (5.0 mmol), and AIBN (20.0 mg) were dissolved in acetonitrile (15.0 mL) and the preassembled solution was added drop by drop, purged with N 2 on ice, and then reacted for 24 h at 60 °C with constant stirring at 100 rpm [30]. Finally, the mesoporous silicon-based magnetic, molecularly-imprinted polymers (Fe 3 O 4 @mSiO 2 @MIPs, abbr.…”

Recent Advances in (Bio)Chemical Sensors for Food Safety and Quality Based on Silver Nanomaterials

“…Since aggregation can be caused by multiple substances found in complex food matrices, Deng et al . ( 109 ) have coupled AgNPs with magnetic molecularly imprinted polymeric microspheres (MMIPs) to improve the selectivity towards caffeine. Although a much lower LOD of caffeine than needed for tea and Coca-Cola samples was obtained (1 µg/L), this sensor does include a previous extraction step.…”

The Theophylline Aptamer: 25 Years as an Important Tool in Cellular Engineering Research

“…While not the focus of this paper, the aptamer has been used to create diagnostic tools through several approaches. Some of these approaches include electrochemical biosensors, − fluorescent reporters, ,,− surface plasmon resonance, − fluorescence resonance energy transfer (FRET), − and quartz crystal microbalances, , among others. − In one interesting set of studies, Lam and Joyce fused the aptamer to cross-replicating RNA enzymes and demonstrated exponential growth of RNA enzymes in the presence of theophylline, but there was no activity when caffeine, theobromine, or trimethyl uric acid were present. − Thus, the aptamer can be a powerful tool not only in cellular engineering, but also in detection and quantification of theophylline in biological and environmental samples.…”