MXene nanosheet loaded gold nanocluster catalytic amplification-aptamer SERS quantitative assay platform for isocarbophos.

The traditional preparation of MXeneTi3C2 is complicated. Two-dimensional MXeneTi3C2 nanosheets were prepared via in-situ generation of HF etching Ti3AlC2 under the microwave irradiation. Gold nanocluster doped nanosheets sol (MXene@Au) with excellent stability and strong catalysis was synthesized with no product residue reducer CO. MXene@Au nanosol can catalyze mandelic acid-HAuCl4 to produce gold nanoparticles, which can be traced via resonance Rayleigh scattering (RRS) and surface-enhanced Raman scattering (SERS). Coupled the dual-mode nanocatalytic indicator reaction with aptamer reaction, a high sensitivity, selectivity, facile SERS/RRS dual-mode biosensnoring assay platform has been constructed for isocarbophos (ICP). The linear range of SERS was 1.0 × 10-3-2.5 × 10-2 nmol/L, with a detection of limit 4.5 × 10-5 nmol/L (S/N = 3). It has been used to detect ICP in water samples, with a good recovery (95.5-104%) and a good relative standard deviation (5.2-9.6%). This new nanocatalytic amplification biosensoring strategy can also assay other organic pesticides including malathion, glyphosate, profenofos and carbendazim. In addition, the nanocatalytic mechanism was investigated.

A novel liquid crystal resonance Rayleigh scattering spectral probe for determination of trace Cr6.

Hexavalent chromium (Cr6+) has strong oxidizing property and toxicity. It has been identified as a carcinogen with obvious carcinogenic effect by the International Anti-cancer Research Center. Therefore, it has a great significance to establish a simple and sensitive method for Cr6+. In the solution, liquid crystal (LC) trans, trans-4-(3,4-difluorophenyl)-4'-n-pentylbicyclohexyl (DP) exhibits strong resonance Rayleigh scattering (RRS) effect due to formation DP nanoparticles. It was used firstly as nanoprobe, to establish a simple and sensitive RRS energy transfer (RRS-ET) method for the determination of trace Cr6+ in water samples. The Cr6+ reacts with diphenylcarbazide (DCB) to produce purple complex. It is adsorbed on the nanoprobe surface, the purple complex as energy receptor and DP as energy donor to produce RRS-ET phenomenon, to make the RRS signal of 370 nm decreasing. In the range of 3-30 nmol/L Cr6+, with the increase of concentration, the RRS signal decreased linearly at 370 nm, with a detection limit of 0.49 nmol/L. This new RRS-ET method was applied to the determination of Cr6+ in water samples, with recovery of 96.0-104.7% and the relative standard deviation (RSD) of 4.44-9.98%.

MXene catalytic amplification-fluorescence/absorption dimode aptamer sensor for the detection of trace Pb2+ in milk.

Lead ion (Pb2+) is a toxic heavy metal, which is very harmful to organisms. Therefore, the establishment of a rapid, simple, and sensitive method is of great significance to food safety and human health. It was found that MXeneTi3C2 nanosheet (NS) has a strong catalytic effect on the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) via H2O2 to form the oxidized product (TMBOX); it has a strong fluorescence peak at 415 nm and an absorption (Abs) peak at 295 nm. The aptamer of Pb2+ (Aptpb) can be adsorbed on the surface of an NS to form MXene-Apt conjugates, which reduces its catalytic active sites and inhibits its catalytic activity. When the target Pb2+ is added, it specifically binds with Aptpb to release MXene NSs to enhance the dimode signals. Therefore, a new MXene catalytic fluorescence/absorption dimode aptamer biosenering platform was fabricated for the determination of trace Pb2+ in milk and water samples, with the fluorescence assay linear range (LR) of 5.0 × 10-2-2.0 nmol/L.

A New Covalent Organic Framework of Dicyandiamide-Benzaldehyde Nanocatalytic Amplification SERS/RRS Aptamer Assay for Ultratrace Oxytetracycline with the Nanogold Indicator Reaction of Polyethylene Glycol 600.

In this paper, dicyandiamide (Dd) and p-benzaldehyde (Bd) were heated at 180 °C for 3 h to prepare a new type of stable covalent organic framework (COF) DdBd nanosol with high catalysis. It was characterized by molecular spectroscopy and electron microscopy. The study found that DdBd had a strong catalytic effect on the new indicator reaction of polyethylene glycol 600 (PEG600)-chloroauric acid to form gold nanoparticles (AuNPs). AuNPs have strong resonance Rayleigh scattering (RRS) activity, and in the presence of Victoria Blue B (VBB) molecular probes, they also have a strong surface-enhanced Raman scattering (SERS) effect. Combined with a highly selective oxytetracycline (OTC) aptamer (Apt) reaction, new dual-mode scattering SERS/RRS methods were developed to quantitatively analyze ultratrace OTC. The linear range of RRS is 3.00 × 10-3 -6.00 × 10-2 nmol/L, the detection limit is 1.1 × 10-3 nmol/L, the linear range of SERS is 3.00 × 10-3-7.00 × 10-2 nmol/L, and the detection limit is 9.0 × 10-4 nmol/L. Using the SERS method to analyze OTC in soil samples, the relative standard deviation is 1.35-4.78%, and the recovery rate is 94.3-104.9%.