A novel gold nanosol SERS quantitative analysis method for trace Na+ based on carbon dot catalysis

Colorimetric-SERS dual-mode sensing of Pb(II) ions in traditional Chinese medicine samples based on carbon dots-capped gold nanoparticles as nanozyme

Peroxidase (POD)-mimicking nanozymes have got great progress in the sensing field, but most nanozyme assaying systems are built with a single-signal output mode, which is vulnerable to the effect of different factors. Thus, establishment of a dual-signal output mode is necessary for acquiring dependable and durable performance. This work described an Fe doped noradrenaline-based carbon dots and Prussian blue (Fe,NA-CDs/PB) nanocomposite as a POD-like nanozyme and modified gold nanoparticles (AuNPs) for the colorimetric and surface-enhanced Raman scattering (SERS) dual-mode sensor of Pb(II) in traditional Chinese medicine samples. With 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 3,3',5,5'-tetramethylbenzidine (TMB) as the substrates, it was found that the addition of Pb(II) inhibited the POD-like activity of Fe,NA-CDs/PB and AuNPs, so it was used for colorimetric and SERS dual-mode assays. The POD-like activity was shown to be a "ping-pong" catalytic mechanism, whereas the addition of Pb(II) produced noncompetitive inhibition with modulatory effects on Fe,NA-CDs/PB. The linear response range for colorimetric and SERS sensor detection of Pb(II) was 0.01-1.00 mg/L with the detection limit of 5 μg/L and 8 μg/L, respectively. This dual-mode detection system shows excellent selectivity. More importantly, the Pb(II) in traditional Chinese medicine samples have successfully assayed with good recovery from 90.4 to 108.9 %.

Aptamer SERS and RRS determination of trace lead ions using nitrogen-doped carbon dot to catalyze the new nano-gold reaction

Nitrogen-doped carbon dots (CDN) were prepared by microwave hydrothermal method using ammonium citrate (AC) and ethylenediaminetetraacetic acid (EDTA) as precursor. It was characterized by transmission electron microscopy (TEM) and infrared spectroscopy (IR). The CDN was found to catalyze the reduction of HAuCl4 to produce gold nanoparticles (AuNP), among which fructose was an effective reducing agent. Using malachite green (MG) as a molecular probe, the surface enhanced Raman scattering (SERS) intensity at 1617 cm-1 and the resonance Rayleigh scattering (RRS) intensity at 375 nm increased linearly with increasing CDN concentration, respectively. The catalytic activity of CDN is inhibited because the aptamer (Apt) can be adsorbed on the surface of the catalyst CDN. The aptamer (Apt)-Pb2+ reaction and CDN-Apt adsorbing reaction were competitive reaction. When there is Pb2+ that binds more tightly to Apt, Apt is desorbed, and the catalytic ability of CDN is restored. Accordingly, an Apt-mediated nanocatalytic amplification SERS/RRS platform for quantitative detection of lead ions was constructed. For the SERS method, the linear range was 0.5-120 nmol/L with DL of 0.11 nmol/L. For the RRS method, the Pb2+ concentration was linear in the range of 50-400 nmol/L with the RRS intensity, and the DL was 15.32 nmol/L. The analysis platform uses CDN catalyzed nanoreactions to generate AuNP products with SERS activity as a substrate, thus overcoming the shortcomings of Pb2+ without scattering activity, and realizing the possibility of SERS and RRS detection of metal ions. It was used for the determination of Pb2+ in real samples with relative standard deviations were 0.94-2.71 % and recovery was 99.00-103.70 %, respectively. In addition, the mechanism of CDN nanoenzyme heterogeneous catalysis of nano-gold reactions was discussed.

Nanogold sol plasmon discattering assay for trace carbendazim in tea coupled aptamer with Au3+-glyoxal-carbon dot nanocatalytic reaction

Carbendazim (CBZ) is a broad-spectrum fungicide, which is toxic to mammals. Therefore, it is very necessary to establish a sensitive detection for food safety. An experiment found that CD_Fe exhibited excellent catalysis for the nano-indicator reaction of HAuCl₄-glyoxal to produce gold nanoparticles (AuNPs) and that the generated AuNPs have a very strong surface-enhanced Raman scattering (SERS) effect at 1613 cm^-1 in the presence of Victoria blue B molecular probes, and resonance Rayleigh scattering (RRS) signals at 370 nm. The aptamer (Apt) suppressed the catalysis of CD_Fe to cause the SERS and RRS signals decreasing. With the addition of CBZ, the specific Apt reaction occurred to restore the catalysis of CD_Fe, and resulting in a linear increase in the signals of RRS and SERS. As a result, this new nanocatalytic amplification indicator reaction was coupled with a specific Apt reaction of carbendazim (CBZ), to construct a new CD_Fe catalytic amplification-aptamer SERS/RRS discattering assay for ultratrace CBZ, which was used to analyze CBZ in tea samples with satisfactory results. In addition, this biosensoring platform can be also used to assay profenofos.

Lysosome-targeted carbon dots for colorimetric and fluorescent dual mode detection of iron ion, in vitro and in vivo imaging

In this work, a colorimetric and fluorescent dual mode sensor based on lysosome-targeted CDs has been desirably implemented to identify Fe³⁺ fluctuations in vitro and in vivo. By simple one-pot hydrothermal carbonization of dried field mint, yellow-fluorescent CDs were directly fabricated without the assistance of other reagents and hold exceptional stability, superior biocompatibility as well as ultra-low cytotoxicity. Results indicated that as-prepared CDs can provide a rapid, reliable, and highly selective recognition of Fe³⁺ with a linear range of 0 μM-400 μM and a detection limit of 0.037 μM. Impressively, it was found that as-developed CDs can successfully target lysosome with high colocalization coefficient (0.85) and responds to fluctuations of Fe³⁺ in living cells. Further, acquired CDs was ingeniously devoted to Escherichia coli imaging. Besides, obtained CDs was eventually utilized to track the variation of Fe³⁺ in vivo system. A preliminary research expresses that as-synthesized CDs can function as an effective tool to detect Fe³⁺ in vitro and in vivo and thus indicates the promising applicability for disease detection in physiology and pathology in the future.

A label-free and carbon dots based fluorescent aptasensor for the detection of kanamycin in milk

A novel label-free aptasensor for kanamycin detection was constructed using gold nanoparticles (AuNPs) as absorber to quench the fluorescence of carbon dots (CDs) via the inner filter effect (IFE). The strategy was mainly relied on the fact that the absorption spectra of AuNPs overlapped with the fluorescence excitation spectra of fluorophores as well as the specific binding capacity of Ky2 aptamer to kanamycin. Upon adding kanamycin antibiotic, the free aptamer sequences are firstly exhausted to form some complexes, which leads to AuNPs aggregation in high salt concentration. Consequently, the absorber's absorption spectrum changes and no longer overlaps with the fluorescence emission spectrum of the CDs, which results in obvious fluorescence recovery of the aptasensor. Herein, the effects of some vital parameters like the type and number of nanoparticles on the fluorescent aptasensor have been investigated. Under optimal conditions, the proposed aptasensor can detect kanamycin in a linear range of 0.04-0.24 μM, with a limit of detection (LOD) as low as 18 nM. Moreover, the further studies also validate the applicability of the proposed aptasensor in milk samples, revealing that it may have enormous potential utility for practical kanamycin detection in food products in the future.

Mesoporous silica supported orderly-spaced gold nanoparticles SERS-based sensor for pesticides detection in food

In this study, a novel sensor fabricated with compactly arranged gold nanoparticles (AuNPs) templated from mesoporous silica film (MSF) via air-water interface has been confirmed as a promising surface-enhanced Raman scattering (SERS) substrate for detecting trace levels of 2,4-dichlorophenoxyacetic acid (2,4-D), pymetrozine and thiamethoxam. The densely arranged AuNPs@MSF had an average AuNPs size of 5.15 nm with small nanogaps (<2nm) between AuNPs, and exhibited a high SERS performance. SERS spectra of pesticides were collected after their adsorption on the AuNPs@MSF. The results showed that the concentration of 2,4-D, pymetrozine and thiamethoxam gave a good linear relationship with SERS intensity. Moreover, the designed SERS-based sensor (AuNPs@MSF) was stable for 3 months with ca. 3% relative standard deviation (RSD) and was applied successfully for the analysis of 2,4-D extraction from both environmental and food samples. The proposed SERS-based sensor was further validated by HPLC and showed satisfactory result (p > 0.05).