A highly selective method of chlortetracycline (CTC) is proposed on the basis of the measurements of total internal reflected resonance light scattering (TIR-RLS) at water/tetrachloromethane (H2O/CCl4) interfaces. In the pH range of 7.54-8.14, the interaction of the binary complex of Eu (III)/CTC in the presence of trioctyl phosphine oxide (TOPO) occurs at the H2O/CCl4 interface, resulting in greatly enhanced TIR-RLS signals with the maximum peak located at 340nm. The enhanced TIRRLS intensity is in proportion to the CTC concentration in the range 0.98～20.0×10-7 mol/L. The limit of detection is 9.8×10-9 mol/L. Synthetic samples and body fluid samples including human urine, human serum, and fresh milk were determined with the recovery of 95.4-106.4% and RSD of 2.9-3.9%.

A novel assay of DNA with a sensitivity at the nanogram level is proposed based on the measurement of enhanced resonance light scattering (RLS) signals resulting from the interaction of Janus Green B (JGB) with DNA. At pH 6.37 and ionic strength<0.20, the RLS signals of JGB were greatly enhanced by DNA in the region of 300-650nm characterized by three peaks at 416.0, 452.0 and 469.2nm. The binding properties were examined using a Scatchard plot based on the measurement of the enhanced RLS data at 416.0nm at a high JGB+DNA molar ratio (R>2.22), and an aggregation mechanism of JGB in the presence of DNA at the nanogram level is proposed. Linear relationships can be established between the enhanced RLS intensity and DNA concentration in the range 0-3.5mg ml21 for both calf thymus DNA (ctDNA) and fish sperm DNA (fsDNA) if 2.0

The features of the three-dimensional (3-D) emission spectrum of the long range assembly of Nile Blue sulfate (NBS) on the molecular surfaces of DNAs were discussed. It was found that the emission signals involve resonance light-scattering (RLS, λRLS=λex), second order light-scattering (SLS, λSLS=2λex), anti-second order light-scattering (ASLS, λASLS=0.5λex), Raman light-scattering (Raman,λRLSR=-49.0+1.28λex, λSLSR=-52.0+0.64λex, and λASLSR=-171.7+2.86λex), and fluorescence (λex=545.0nm, λem=610.0nm). The wavelengths of all light-scattering signals keep linear relationships with at of the incident light beam (λex), and the intensities of the light-scattering signals in the 3-D spectrum are in the order: IRLS>ISLS>IASLS>IRLSR>ISLSR>IASLSR. At pH 7.20-7.80 and ionic strength 0.012, these signals, including RLS, SLS, and ASLA, were found to be strongly enhanced because of the long range assembly of NBS on the molecular surface of both calf thymus DNA (ctDNA) and Æsh sperm DNA (fsDNA). Fluorescence quenching of NBS by DNAs occurs, but no signiÆcantly enhanced Raman light-scattering signals of NBS can be detected in the long range assembly. By independently using the enhanced intensity of RLS at 293.8nm (λex=293.8nm), ASLS intensity at 293.8nm (λex=587.6nm), or SLS intensity at 587.6nm (λex=293.8nm), ctDNA and fsDNA at nanogram levels can be determined with identical results.

The supramolecular interaction of nile blue sulphate (NBS) with nucleic acids was studied by investigating the characteristics of the interaction absorption spectra on the basis of the drug binding process in organic system in which small amount of drug interacting with large amount of biological macromolecules involves, and an accordingly binding model for organic dyes with large amount of macromolecules was established. At pH 7.40 and ionic strength 0.004, the H-aggregation of NBS occurs with increasing NBS concentration. The NBS aggregates can be bound to both calf thymus DNA and fish sperm DNA by the ratio of each nucleotide residue with a molecule of NBS if the concentration of DNAs is more than 15-fold excessive. The corresponding binding constant for the interaction of NBS with DNAs is about 103 order, with which thermodynamic parameters for the interactions, such as the change of free energy, enthalpy and entropy at 25℃, were calculated. It was found that the binding of NBS with thermally denatured DNA is similar to that with native yeast RNA, which indicates H-aggregation of NBS can be encouraged by single stranded nucleic acids.

A method of protein determination with the limit of determination at nanogram levels is proposed by using a common spectrofluorometer to detect the intensity of preresonance light-scattering (PRLS). In the pH range 1.81-4.10, the interactions of α,β,γ,δ-tetrakis (5-sulfothienyl)-porphine, T (5-ST) P, with proteins were studied. It was found that the interactions result in a strongly enhanced preresonance light-scattering signal at 472.0nm. Mechanism studies showed that the enhanced preresonance light-scattering stems from the J-aggregation of T (5-ST) P in the presence of proteins. It was found that the J-aggregation process is speedy and is scarcely affected by temperature, which supplies a precise method for the determination of proteins. Different proteins in the range 0-7mg ml21 can be determined with the limits of determination below 100ng ml21 depending on the concentration of T (5-ST) P. The results of determination for synthetic samples were in agreement with the desired values, and the ones for human serum samples were identical to those obtained according to the Bradford method using CBB G-250.