A novel method for the determination of total protein in human serum by near infrared fluorescence recovery

Manipulating the monomer-dimer transformation of a heptamethine cyanine ligand: near infrared chromogenic recognition of biothiols

A novel absorbance recovery method has been developed for the determination of biothiols with a near-infrared reagent. This method employs a two-reagent system composed of cation heptamethine cyanine (CyL) and Hg²⁺. The absorbance of CyL, with a maximum peak at 760 nm, was decreased due to addition of Hg²⁺, but recovered when biothiols were added. Under optimal conditions, the reciprocal extent of recovered absorbance was proportional to the concentration of biothiols. The calibration curves are linear over the range of (0.3-7.0) × 10^-6 M for cysteine, (1.0-10.0) × 10^-6 M for homocysteine and (1.0-9.0) × 10^-6 M for glutathione. Because of the specific affinity of Hg²⁺for biothiols, there is minimal interference from other amino acids. This method has been successfully applied to the determination of homocysteine in human urine samples with satisfactory results.

Determination of nucleic acids with a near infrared cyanine dye using resonance light scattering technique

A new method for the determination of nucleic acids has been developed based on the enhancement effect of resonance light scattering (RLS) with a cationic near infrared (NIR) cyanine dye. Under the optimal conditions, the enhanced RLS intensity at 823 nm is proportional to the concentration of nucleic acids in the range of 0-400 ng mL-1 for both calf thymus DNA (CT DNA) and fish sperm DNA (FS DNA), 0-600 ng mL-1 for snake ovum RNA (SO RNA). The detection limits are 3.5 ng mL-1, 3.4 ng mL-1 and 2.9 ng mL-1 for CT DNA, FS DNA and SO RNA, respectively. Owing to performing in near infrared region, this method not only has high sensitivity endowed by RLS technique but also avoids possible spectral interference from background. It has been applied to the determination of nucleic acids in synthetic and real samples and satisfactory results were obtained.

Proton T1 and T2 relaxivities of serum proteins

In the present study, T(1) and T(2) of phantoms containing serum sets with varying amounts of proteins, serum samples with certain amounts of proteins, serum diluted by distilled water, and serum treated with iron were measured. In addition, T(1) and T(2) of phantoms containing normal serum, diluted serum, and albumin-doped serum were also measured. Relaxation rates were plotted versus protein concentrations. The slope of relation was taken as relaxivity. The T(1) relaxivities of proteins were ranged from 0.035 to 0.080 s(-1)(g/dl)(-1), whereas T(2) relaxivities were ranged from 0.24 to 0.68 s(-1)(g/dl)(-1). The T(1) and T(2) relaxivities of transferrin iron were 2.40 and 2.60 mM(-1)s(-1), respectively. The contributions of diamagnetic proteins and transferrin iron to the relaxation rate of serum were also calculated for each of diluted serum, normal and albumin-doped serum. The contributions and the average TP relaxivities(calculated by using individual relaxivities and the ratios of protein fractions in TP) were used for TP calculations. The agreement between the calculated TP and TP by autoanalyzer and also the agreement between average TP relaxivities and the TP relaxivities determined from dilution experiments show that the data of relaxivities are reliable. The results suggest that individual protein relaxivities explain the influence of serum TP composition on T(1) and T(2) relaxation times.

Determination of Nucleic Acids by Near-Infrared Fluorescence Quenching of Hydrophobic Thiacyanine Dye in the Presence of Triton X-100

A near-infrared (near-IR) fluorescence quenching method was developed for the determination of nucleic acids in aqueous solution by using a cationic heptamethylene thiacyanine as a probe. The near-IR cationic cyanine showed maximum excitation and emission wavelengths at 800 and 825 nm, respectively, in the presence of Triton X-100; the fluorescence of the cyanine could be greatly quenched by DNA. The calibration graphs were linear over the range of 10-400 ng/mL for CT (calf thymus) DNA and over the range 5-400 ng/mL for FS (fish sperm) DNA under optimal conditions. The corresponding detection limits were 5.2 ng/mL for CT DNA and 2.5 ng/mL for FS DNA. The relative standard deviation (n = 8) was 3.1% for 75 ng/mL CT DNA and 2.2% for 75 ng/mL FS DNA, respectively. Preliminary research showed that the fluorescence quenching might be ascribed to the formation of dye aggregate facilitated by DNA.

Dye-binding protein assay using a long-wave-absorbing cyanine probe

A simple and fast protein assay that involves the binding of water-soluble sulfonate heptamethylene cyanine to protein is described. The binding of the dye to protein causes a shift in the absorption maximum of the dye from 778 to 904 nm, and the increase in absorption at 904 nm is monitored. This assay is very reproducible, of good color stability for at least 80 min, and sensitive at the 100 ng/mL level of human serum albumin (HSA) when a spectrophotometer with near-infrared wavelength is used to measure absorbance. Few chemicals except ionic surfactants such as cetyltrimethylammonium bromide and sodium dodecyl sulfonate interfere with the assay. Purified proteins have different capacities to interact with the dye; under the experimental conditions, the linear ranges of bovine serum albumin (BSA), HSA and gamma-IgG were 200-2000, 100-2400, and 200-3000 ng/mL, respectively. The relative standard deviation for the five replicate determinations of 1200 ng/mL BSA is 2.1%.