Single-atom Fe catalytic amplification-gold nanosol SERS/RRS aptamer as platform for the quantification of trace pollutants.

Bisphenol A (BPA), as a typical endocrine disruptor, poses a serious threat to human health. Therefore, it is urgent to establish a rapid, sensitive, and simple method for the determination of BPA. In this paper, based on the aptamer-mediated single-atom Fe carbon dot catalyst (SAFe) catalyzing the HAuCl4-ethylene glycol (EG) nanoreaction, a new SERS/RRS di-mode detection method for BPA was established. The results show that SAFe exhibits a strong catalytic effect on the HAuCl4-EG nanoreaction, which could generate purple gold nanoparticles (AuNPs) with resonance Rayleigh scattering (RRS) signals and surface-enhanced Raman scattering (SERS) effects. After the addition of BPA aptamer (Apt), it could encapsulate SAFe through intermolecular interaction, thus inhibiting its catalytic action, resulting in the reduction of AuNPs generated and the decrease of RRS and SERS signals of the system. With the addition of BPA, Apt was specifically combined with BPA, and SAFe was re-released to restore the catalytic ability; the generated AuNPs increased. As a result of this RRS and SERS signals of the system recovered, and their increment was linear with the concentration of BPA. Thus, the quantification of 0.1-4.0 nM (RRS) and 0.1-12.0 nM (SERS) BPA was realized, and the detection limits were 0.08 nM and 0.03 nM, respectively. At the same time, we used molecular spectroscopy and electron microscopy to study the SAFe-HAuCl4-ethylene glycol indicator reaction, and proposed a reasonable SAFe catalytic reaction mechanism. Based on Apt-mediated SAFe catalysis gold nanoreaction amplification, a SERS/RRS di-mode analytical platform was established for targets such as BPA.

A label-free DNAzyme-cleaving fluorescence method for the determination of trace Pb(2+) based on catalysis of AuPd nanoalloy on the reduction of rhodamine 6G.

The substrate chain of double-stranded DNA (dsDNA) could be specifically cleaved by Pb(2+) to release single-stranded DNA (ssDNA) that adsorbs onto the AuPd nanoalloy (AuPdNP) to form a stable AuPdNP-ssDNA complex, but the dsDNA can not protect AuPdNPs in large AuPdNP aggregates (AuPdNPA) under the action of NaCl. AuPdNP-ssDNA and large AuPdNPA could be separated by centrifugation. On increasing the concentration of Pb(2+) , the amount of released ssDNA increased; AuPdNP-ssDNA increased in the centrifugation solution exhibiting a catalytic effect on the slow reaction of rhodamine 6G (Rh6G) and NaH2 PO2 , which led to fluorescence quenching at 552 nm. The decrease in fluorescence intensity (ΔF) was linear to the concentration of Pb(2+) within the range 0.33-8.00 nmol/L, with a detection limit of 0.21 nmol/L. The proposed method was applied to detect Pb(2+) in water samples, with satisfactory results.

A new SERS quantitative analysis strategy for ultratrace chloramphenicol with Fe3O4@MIP nanocatalytic probe.

Three functional magnetic nanocatalytic probe, which integrates recognition, catalytic amplification, and separation enrichment, is a new approach to construct a simple, fast, highly selective, and sensitive analytical method. In this article, a new magnetic nanosurface molecularly imprinted polymer nanoprobe (Fe3O4@MIP) with trifunctionality was rapidly prepared using a microwave-assisted method with magnetic Fe3O4 nanoparticles as a substrate, chloramphenicol (CAP) as a template molecule, and methacrylic acid as a functional monomer. The characterized nanoprobe was found that could specifically recognize CAP, strongly catalyze the new indicator nanoreaction of fructose (DF)-HAuCl4. The gold nanoparticles (AuNPs) exhibit strong resonance Rayleigh scattering (RRS) and surface enhanced Raman scattering (SERS) effects. Upon addition of CAP, the SERS/RRS signals were linearly weakened. Accordingly, a new SERS/RRS analysis platform for highly sensitive and selective determination of CAP was constructed. The SERS linear range was 0.0125-0.1 nmol/L, with detection limit (DL) of 0.004 nmol/L CAP. Furthermore, it could be combined with magnet-enriched separation to further improve the sensitivity, with a DL of 0.04 pmol/L CAP. The SERS method has been used for the determination of CAP in real samples, with relative standard deviations of 2.37-9.89 % and the recovery of 95.24-107.1 %.

On-signal amplification of silver nanosol RRS/SERS aptamer detection of ultratrace urea by polystyrene nanosphere catalyst.

The catalytic amplification signal of polystyrene nanosphere (PN) is used to conveniently fabricate the resonance Rayleigh scattering (RRS)/surface-enhanced Raman scattering (SERS) dual-mode method to sensitively and selectively detect urea in food. PN has strong catalysis of the slow nanoreaction of citrate-Ag(I) to produce yellow silver nanoparticles (AgNP), which exhibit strong RRS effect and SERS effect with molecular probes. When aptamer (Apt) is present, the Apt is adsorbed on the PN surface, the catalysis is weakened, the AgNP is reduced, and the SERS/RRS signal is weakened. After adding urea to exhibit specific Aptamer reaction, the Apt is desorbed from the PN surface and the catalysis is restored. As urea increase, the desorbed PNs increase to produce more AgNPs indicator to increase SERS/RRS signal. The increase value △I of SERS/RRS is linearly to urea concentration. Therefore, a sensitive and selective SERS/RRS dual-mode method for urea is established based on aptamers-regulated the catalysis of PNs. This method is applied to the detection of urea in milk with satisfactory results. The relative standard deviation is 3.9-6.8% and the recovery rate is 94.5-102%.

A highly sensitive resonance scattering spectral assay for carcinoembryonic antigen using immunonanogold as probe and nanocatalyst of NH2(OH-Cu(II) particle reaction.

Nanogold of 10 nm was used to label carcinoembryonic antigen antibody (CEAAb) to prepare a probe (Au-CEAAb) for carcinoembryonic antigen (CEA). In a Na2HPO4-NaH2PO4 buffer solution of pH 6.8, CEA reacted with Au-CEAAb to form a big Au-CEAAb-CEA immunocomplex that can be removed by centrifugation. The unreacted Au-CEAAb in the centrifugal supernatant exhibited catalytic effect on the Cu2O particle reaction, and the Cu2O particles displayed a resonance scattering (RS) peak at 602 nm. When CEA increased, the RS intensity at 602 nm decreased, and the decreased RS intensity (ΔI (602 nm)) was linear to CEA concentration (C (CEA)) in the range of 0.02-12 ng mL(-1), with the regression equation of ΔI (602 nm) = 27.1 C (CEA) + 3.3, correlation coefficient of 0.9978 and detection limit of 3 pg mL(-1) CEA. The proposed method was applied to detect CEA in real samples, with satisfactory results.

Aptamer-Regulated Gold Nanosol Plasmonic SERS/RRS Dimode Assay of Trace Organic Pollutants Based on TpPa-Loaded PdNC Catalytic Amplification.

As with excellent catalytic performance, palladium nanoclusters (PdNCs) have a wide range of applications. However, the traditional PdNCs are easy to agglomerate in the analysis system and lose their catalytic activity. A covalent organic framework (COF) has a definite structure, good stability, and easy surface functionalization. So, it is of great significance to develop stable PdNCs with high catalytic activity and then combine with advanced analysis techniques to analyze ultratrace small-molecule pollutants in the environment. In this research, a stable PdNC dispersed on a COF (PdTpPa) catalyst is prepared and we find it with strong catalysis for the NaH2PO2-HAuCl4 catalytic reaction. Furthermore, this nanocatalytic indicator reaction can be tracked by surface-enhanced Raman spectroscopy (SERS) and resonance Rayleigh scattering (RRS) dual-mode. Combined with a highly specific aptamer-modifying technique, a highly sensitive and selective SERS/RRS dimode assay platform for trace organic pollutants has been developed. The detection limits of oxytetracycline (OTC), glyphosate (GLY), tetracycline (TEC), and bisphenol A (BPA) are 0.64, 0.03, 6.2 × 10-3, and 0.53 × 10-3 ng/mL, respectively. This work also provides ideas for the application of COF materials and Pd nanocatalysts in the molecular spectral detection of trace pollutants.

A simple resonance Rayleigh scattering method for determination of trace CA125 using immuno-AuRu nanoalloy as probe via ultrasonic irradiation.

AuRu nanoalloy (GR) with Au/Ru molar ratio of 32/1 was prepared by the sodium borohydride reduction method. It was used to label the CA125 antibody (Ab) to obtain an immunonanoprobe (GRAb) for cancer antigen 125 (CA125). In pH 7.0 citric acid-Na2HPO4 buffer solution and irradiation of ultrasound, the probes were aggregated nonspecifically to big clusters that showed a strong resonance Rayleigh scattering (RRS) peak at 278 nm. Upon addition of CA125, GRAb reacted specifically with CA125 to form dispersive immunocomplexes of CA125-GRAb in the solution and this process enhanced by the ultrasonic cavitation effect, which led to the RRS intensity decreased greatly. The decreased RRS intensity was linear to the concentration of CA125 in the range of 1.3-80 U/mL, with a detection limit of 0.6 U/mL. The proposed method was applied to detect CA125 in real sample, with satisfactory results.

Highly sensitive and selective determination of fluorine ion by graphene oxide/nanogold resonance Rayleigh scattering-energy transfer analytical platform.

In pH 4.0 acetate buffer solution, fluorine ions react with fluorine reagent (FR) and La(III) to generate blue ternary complex that exhibited strong absorption at about 370 nm. Upon addition of graphene oxide/nanogold (GO/NG) as resonance Rayleigh scattering (RRS) spectral probe with strong RRS peak at 370 nm, the color changed to gray, and the RRS intensity decreased with the increase of fluorine ion concentration due to the RRS energy transfer (RRSET) from GO/NG to the complex. Under the selected condition, the decreased RRS peak ΔI370 nm was linear to fluorine ion concentration in the range of 6.0 × 10(-8)-1.3 × 10(-5)mol/L, with a detection limit of 3.0 × 10(-8)mol/L F(-). This RRSET method was applied to the analysis of fluorine in toothpaste and water samples, with satisfactory results.