In the 0.02 mol/L HCl medium solution, berberine (BB) cationic ion and AuI2- combine to BB-AuI2 association complex molecule. These complex molecules self-aggregate to (BB-AuI2)n association particles. It exhibits a fluorescence peaks at 470 nm. A new and sensitive fluorescence method has been proposed for the determination of trace amounts of BB in the range of 10-800 ng/ml. The detection limit is 3ng/ml BB. The method has been applied to the determination of trace berberine in real samples, with satisfactory results. The cause of the fluorescence was also discussed.

In the medium of HCl containing KI, acridine red (AR) exhibited a fluorescence peak at 550 nm, and acridine ornage (AO) has a fluorescence peak at 520 nm. Upon addition of IO3-, it reacts with excessive I- to form I3-. The AR and I3- combine to form an association particle that caused fluorescence quenching at 550 nm. IO3- concentration in the range of 5.0-120×10-7 mol/L can be determined by AR fluorescence quenching method.

In acidic condition, NO2- combined with p-aminobenzene sulfonic acid by diazotization, and then reacted with α-naphthylamine to form purple azo dye. The resonance Rayleigh scattering (RRS) signal of the color system was detected by nanogold probe. Under the chosen conditions, the decreased RRS intensity ΔI (ΔI= Ib - I) at 500 nm was linear to the NO2- concentration in the range of 7.0×10-2-42.0μmol/L, with a regression equation of ΔI=6.72 C - 6.93, a correlation coefficient of 0.9982 and a detection limit of 2.6×10-4 mol/L NO2-.

Under the conditions of HCl-KI, acridine red (AR) has a max absorption peak at 540 nm, the max absorption peak of acridine orange (AO) at 480 nm. When there is IO3-, it reacts with excessive I-to form I3-. The AR and I3-all combine to form an association particle that caused the absorption decreasing. I03-concentration in the range of 5-90×10-7mol/L can be determined by the pectrophotometry.

In HCl solution, the Se (IV) was reduced to SeH2 by NaBH4, and absorbed by solution of ethanol-AgNO3. The Ag+ was reduced to nanosilver that exhibited surface plasmon resonance absorption (SPR) peaks at 292 nm and 420 nm. Under the selected conditions, the value at 292 nm was linear to the concentration of Se (IV) in the range of 0.08-2.0 μg/mL, a detection limit of 0.04 μg/mL. The proposed method was applied to detect Se (IV) in water samples, with satisfactory results.