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A new method for detecting protein by synchronous fluorescence enhancement was developed, based on the combination of near infrared (NIR) fluorescence and the dedimerization phenomenon of methylene blue (MB). Under analytical conditions, there are linear relationships between the enhancing extent of synchronous fluorescence of MB-sodium dodecyl benzene sulfonate (SDBS)-protein at 667nm and the concentration of protein in the range of 8.0x10(-8)-4.0x10(-5)gmL(-1) for bovine serum albumin (BSA), 1.0x10(-7)-3.5x10(-5)gmL(-1) for egg albumin (EA). The detection limits (S/N=3) of BSA and EA are 8.9ngmL(-1) and 10.0ngmL(-1), respectively. The fluorescence enhancement mechanism is discussed in detail. Results from multiple techniques indicate that the fluorescence enhancement of the system originates from the hydrophobic microenvironment provided by BSA and SDBS, and the formation of an MB-SDBS-BSA complex, as well as the deaggregation of some MB dimer.

In this paper, a sensitive resonance light scattering (RLS) method for the determination of protein is reported. In the Tris-HCl (pH 7.50) buffer, protein enhanced the RLS intensity of the Y(3+)-2-thenoyltrifluoroacetone (TTA)-sodium dodecyl sulphate (SLS) system. The enhanced RLS intensities were in proportion to the concentrations of proteins in the range 8.0 x 10(-9)-1.0 x 10(-5) g/mL for BSA, 1.0 x 10(-8)-1.0 x 10(-5) g/mL for HSA and 1.0 x 10(-8)-1.0 x 10(-6 )g/mL for EA, and their detection limits were 5.0, 5.4 and 6.7 ng/mL, respectively. Actual samples were satisfactorily determined. The interaction mechanism was also studied., ((c) 2008 John Wiley & Sons, Ltd.)

The fluorescence of acridine orange (AO) is greatly quenched by the anionic surfactant sodium dodecyl benzene sulphonate (SDBS), but when protein is added into the AO-SDBS system, the fluorescence intensity of the latter is enhanced again. Based on this, a new fluorimetric method of determination of protein was developed. Under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of protein, such as bovine serum albumin (BSA), human serum albumin (HSA) and egg albumin (EA), over a wide range with detection limits at the 10(-9) g/mL level. This method has been satisfactorily used for the determination of protein in samples. We compared results using 280 nm and 490 nm excitation wavelengths and the mechanism of the assay., (Copyright (c) 2006 John Wiley & Sons, Ltd.)

Resonance light scattering (RLS) of Congo red (CR) was greatly enhanced by BSA (HSA) in the presence of Triton X-100 (TX-100). In sodium citrate-HCl buffer (pH 2.7-3.0), the enhanced intensity of resonance light scattering at 360 nm was in proportion to the concentration of proteins [corrected] The linear relationship was obtained between the resonance light scattering intensity and proteins in the range 5.0 x 10(-8)-8.0 x 10(-6) g/mL and 1.0 x 10(-9)-6.0 x 10(-6) g/mL for BSA and HSA, respectively. Their detection limits were 1.4 x 10(-8) g/mL and 2.8 x 10(-10) g/mL (S:N = 3), respectively. Synthetic and actual samples were analysed satisfactorily.

Chlorotetracycline (CTC) can react with europium ions Eu3+, and the complex emits the intrinsic fluorescence of Eu3+. The intensity is greatly enhanced by proteins and this forms the basis of a new fluorimetric method for determination of protein. Further research indicates that under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins, in the range 2.0 x 10(-7)-1.0 x 10(-5) g/mL for bovine serum albumin (BSA) (linear equation, I(f) = 34.35933 + 11.54467 x 10(6)C)(r = 0.99895) and 8.0 x 10(-7)-1.0 x 10(-5) g/mL for human serum albumin (HSA) (linear equation, I(f) = 76.58881 + 5.3569 x 10(6)C) (r = 0.99283). Detection limits (S/N = 3) were 8.9 x 10(-9) g/mL for BSA and 3.3 x 10(-8) g/mL for HSA. In an assay for BSA in calf serum, this method gave a value close to that determined by the UV spectrophotometric method.

The co-luminescence effect in a terbium-gadolinium-protein-sodium dodecyl benzene sulfonate (SDBS) system is reported here. Based on it, the sensitive quantitative analysis of protein at nanogram levels is established. The co-luminescence mechanism is studied using fluorescence, resonance light scattering (RLS), absorption spectroscopy and NMR measurement. It is considered that protein could be unfolded by SDBS, then a efficacious intramolecular fluorescent energy transfer occurs from unfolded protein to rare earth ions through SDBS acting as a "transfer bridge" to enhance the emission fluorescence of Tb3+ in this ternary complex of Tb-SDBS-BSA, where energy transfer from protein to SDBS by aromatic ring stacking is the most important step. Cooperating with the intramolecular energy transfer above is the intermolecular energy transfer between the simultaneous existing complexes of both Tb3+ and Gd3+. The fluorescence quantum yield is increased by an energy-insulating sheath, which is considered to be another reason for the resulting enhancement of the fluorescence. Förster theory is used to calculate the distribution of enhancing factors and has led to a greater understanding of the mechanisms of energy transfer.

Spectral probes (or labels) have been widely used for the investigation and determination of proteins and have made considerable progress. Traditional luminescence probes include fluorescent derivatizing reagents, fluorescent probes and chemiluminescence probes which continue to develop. Of them, near infrared (NIR) fluorescent probes are especially suitable for the determination of biomolecules including proteins, so their development has been rapid. Novel luminescence probes (such as nanoparticle probes and molecular beacons) and resonance light scattering probes recently appeared in the literature. Preliminary results indicate that they possess great potential for ultrasensitive protein detection. This review summarizes recent developments of the above-mentioned probes for proteins and 195 references are cited.

The 15∼25 nm water soluble and stable gold nanoparticles were synthesized and studied for their spectral properties and interactions with proteins. Results showed that 15 nm gold nanoparticles can emit near infrared fluorescence with an emission peak of 811.2 nm under the excitation of 538 nm. The study also showed that proteins can obviously enhance the near infrared fluorescence intensity of gold nanoparticles. Under the optimized conditions, there is a linear relationship between the fluorescence intensity enhancement of the system and the concentrations of the proteins, which can be used in a new method for the determination of trace proteins. The mechanisms of the interaction and the fluorescence enhancement of the nano-gold-protein system were also studied. [ABSTRACT FROM AUTHOR]

Abstract: It is found that rutin can react with yttrium(III) (Y3+), and emits fluorescence of rutin. The intensity is greatly enhanced by proteins in the presence of sodium lauryl sulfate (SLS). Based on this, a new fluorimetric method of determination of proteins is developed. Under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins in the range of 5.0×10−9–1.0×10−5 g/mL for bovine serum albumin (BSA), 3.0×10−8–1.0×10−5 g/mL for human serum albumin (HSA) and 1.0×10−7–2.0×10−5 g/mL for egg albumin (EA). Their detection limits () are 1.6×10−9, 9.8×10−9 and 2.1×10−8 g/mL, respectively. The interaction mechanism is also studied. [Copyright &y& Elsevier]

It was found that the fluorescence intensity of lanthanum (III) (La 3+ )-quercetin (Qu) complex is greatly enhanced by proteins in the presence of sodium dodecyl benzene sulfonate (SDBS). Based on this finding, a new fluorimetric method for the determination of proteins was developed. Under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins in the range of 2.5×10 -8 to 1.0×10 -5 g/mL for bovine serum albumin (BSA), 5.0×10 -8 to 1.5×10 -5 g/mL for human serum albumin (HSA), and 1.0×10 -7 to 1.5×10 -5 g/mL for egg albumin (EA). Their detection limits (S/N=3) are 5.0×10 -9 g/mL, 7.0×10 -9 g/mL, and 2.1×10 -8 g/mL, respectively. The interaction mechanism was also studied. [ABSTRACT FROM AUTHOR]

Abstract: It is found that the fluorescence intensity of morin–Al3+ complex can be greatly enhanced by proteins in the presence of cetyltrimethylammonium bromide (CTAB). It is considered that protein and CTAB provide a hydrophobic environment with low polarity and large viscosity, resulting in the fluorescence enhancement of morin–Al3+ complex. The experiments indicate that under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins (such as bovine serum albumin (BSA), human serum albumin (HSA) and egg albumin (EA)) in the wide range, and their detection limits (S/N=3) are 2.6×10−9, 1.4×10−8 and 1.6×10−8 gml−1, respectively. This method has satisfactorily been used for the determination of protein in actual sample. In comparison with most of fluorimetric methods reported, this method is quick and simple, and has high sensitivity, wide linear range and good stability. [Copyright &y& Elsevier]

Abstract: It is found that protein and sodium dodecyl sulphonate (SDS) can enhance resonance light scattering (RLS) of curcumin (CU). Based on this phenomenon, a new quantitative method for protein in aqueous solution has been developed. In the BR (pH 3.5) buffer, the RLS intensity of CU–SDS system is greatly enhanced by protein. The enhanced RLS is proportional to the concentration of protein in the range of 0.00020–20.0μgml−1 for bovine serum albumin (BSA) and 0.00040–1.0μgml−1 for human serum albumin (HSA) and their detection limits are 0.16 and 0.041ngml−1, respectively. An actual sample is satisfactorily determined. In addition, the interaction mechanism between protein and CU–SDS is also studied by using multi-techniques such as RLS, absorption spectroscopy and fluorescence, zeta potential assay measurement. [Copyright &y& Elsevier]

Abstract: A new resonance light scattering (RLS) assay of protein is presented. In Tris–NaOH (pH = 10.93) buffer, the RLS of rutin–cetylpyridine bromide (CPB) system can be greatly enhanced by protein, including bovine serum albumin (BSA) and human serum albumin (HSA). The enhanced RLS intensities are in proportion to the concentration of proteins in the range of 5 × 10-9 to 2.5 × 10-6gml-1 for BSA and 2.5 × 10-8 to 3.5 × 10-6gml-1 for HSA. The detection limits (S/N = 3) are 3.0ngml-1 for BSA and 10.0ngml-1 for HSA. Samples are determined satisfactorily. [Copyright &y& Elsevier]

A new determination method of proteins with the limit of determination at nanogram levels is proposed by using a common spectrofluorimeter to detect intensity of resonance double line scattering (RDLS). Proteins including bovine serum albumin (BSA), human serum albumin (HSA) can combine with morin and cetyltrimethylammonium briomide (CTMAB) in the pH range 7.0–8.0 and produce enhanced RDLS signal at λex/λem=305.0/610.0 nm. Optimization conditions for the morin–protein–CTMAB interaction were tested. In the studied system, BSA/CTMAB/morin=1:2:3. The association constant of morin with BSA is 5.2×104. Under the optimum conditions, the linear range is 7.5×10−8–1.0×10−5 g/ml for BSA, 2.5×10−8–5.0×10−6 g/ml for HSA. The detection limits (S/N=3) are 66.0 ng/ml for BSA and 23.0 ng/ml for HSA, respectively. Four synthetic samples were analyzed satisfactorily. [ABSTRACT FROM AUTHOR]

Abstract: It was found that oxolinic acid (OA) at high concentration can self-assemble into nano- to micro- meter scale OA aggregates in Tris–HCl (pH 7.48) buffer solution. The nanoparticles of OA were adopted as fluorescence probes in the quantitative analysis of proteins. Under optimum conditions, the fluorescence quenching extent of nanometer scale OA aggregates was in proportion to the concentration of albumins in the range of 3.0×10−8 to 3.0×10−5 gmL−1 for bovine serum albumin (BSA) and 8.0×10−8 to 8.0×10−6 gmL−1 for human serum albumin (HSA). The detection limits (S/N=3) were 3.4×10−9 gmL−1 for BSA, and 2.6×10−8 gmL−1 for HSA, respectively. Samples were satisfactorily determined. The interaction mechanism of the system was studied using fluorescence, UV–vis, resonance light scattering (RLS) and transmission electron microscope (TEM) technology, etc., indicating that the nonluminescent complex was formed between serum albumin molecular and OA, to disaggregate the self-association of OA, which resulted in the dominated static fluorescence quenching in the system. [Copyright &y& Elsevier]