Mercury (Hg) is a heavy metal pollutant, there is an urgent need to develop simple and sensitive methods for Hg(II) in water. In this article, a simple and sensitive resonance Rayleigh scattering (RRS) method was developed for determination of 0.008–1.33 µmol/L Hg, with a detection limit of 0.003 μmol/L, based on the Hg(II) regulation of gold nanoenzyme catalysis on the HAuCl₄-H₂O₂ to form gold nanoparticles (AuNPs) with an RRS peak at 370 nm. Upon addition of molecular probes of Victoria blue B (VBB), the surface-enhanced Raman scattering (SERS) peak linearly decreased at 1612 cm⁻¹ with the Hg(II) concentration increasing in the range of 0.013–0.5 μmol/L. With its good selectivity and good accuracy, the RRS method is expected to be a promising candidate for determining mercury ions in water samples.

The strongly fluorescent and highly catalytic N-doped carbon dots (CD_N) were rapidly prepared by a microwave irradiation procedure and were characterized by electron microscopy (EM), laser scattering, infrared spectroscopy (IR), and by their fluorescence spectrum. It was found that the CD_N had a strong catalytic effect on the fluorescence reaction of 3,3′,5,5′-tetramethylbenzidine hydroxide ((TMB)–H₂O₂) which produced the oxidation product of TMB (TMB_OX) with strong fluorescence at 406 nm. The aptamer (Apt) was adsorbed on the CD_N surfaces which weakened the fluorescence intensity due to the inhibition of catalytic activity. When the target molecule isocarbophos (IPS) was added, it reacted with the Apt to form a stable conjugate and free CD_N which restored the catalytic activity to enhance the fluorescence. Using TMB_OX as a fluorescent probe, a highly sensitive nanocatalytic method for determination of 0.025–1.5 μg/L IPS was established with a detection limit of 0.015 μg/L. Coupling the CD_N fluorescent probe with the Apt–IPS reaction, a new CD fluorescence method was established for the simple and rapid determination of 0.25–1.5 μg/L IPS with a detection limit of 0.11 μg/L.

The blue triangle nanosilver (BAgNP) sol was prepared by the two reducers of NaBH₄ and H₂O₂. Using BAgNP as the precursor, a small spherical nanosilver (AgNP) sol in yellow was synthesized by addition of suitable amounts of X ⁻ (X = Cl, Br, and I). The oxidization process of BAgNP to AgNP was studied in detail by resonance Rayleigh scattering (RRS), surface-enhanced Raman scattering (SERS), laser scattering, surface plasmon resonance (SPR) absorption, and microscope techniques. It has been observed that NaCl accelerated the oxidizing BAgNP to form AgNP, and an oxidizing mechanism and quasi-nanograting Raman-scattering enhanced mechanism were developed to explain the phenomena. Using the BAgNP sol as substrate and based on the catalysis of Ti(IV) on the BrO₃ ⁻ oxidizing safranine T (ST) molecular probe with a strong SERS peak at 1,535 cm⁻¹, a new catalytic SERS quantitative method was developed for the determination of 1.0 to 100 ng/mL Ti, with a detection limit of 0.4 ng/mL.