Chitosan-capped gold nanoparticles for selective and colorimetric sensing of heparin.

In this contribution, novel chitosan-stabilized gold nanoparticles (AuNPs) were prepared by mixing chitosan with citrate-reductive AuNPs under appropriate conditions. The as-prepared chitosan-stabilized AuNPs were positively charged and highly stably dispersed in aqueous solution. They exhibited weak resonance light scattering (RLS) intensity and a wine red color. In addition, the chitosan-stabilized AuNPs were successfully utilized as novel sensitive probes for the detection of heparin for the first time. It was found that the addition of heparin induced a strong increase of RLS intensity for AuNPs and the color change from red to blue. The increase in RLS intensity and the color change of chitosan-stabilized AuNPs caused by heparin allowed the sensitive detection of heparin in the range of 0.2-60 µM (~6.7 U/mL). The detection limit for heparin is 0.8 µM at a signal-to-noise ratio of 3. The present sensor for heparin detection possessed a low detection limit and wide linear range. Additionally, the proposed method was also applied to the detection of heparin in biological media with satisfactory results.

Resonance light scattering technique as a new tool to determine the binding mode of anticancer drug oridonin to DNA.

In this study, a sensitive and reliable assay has been developed to determine the binding mode of oridonin to DNA in vitro using resonance light scattering (RLS) technique. The binding mode of ORI with DNA has been confirmed by measuring the changes of RLS intensity under different pH and ionic strength. It is the ORI that is intercalated into the double helix DNA to destroy its template function and inhibit the synthesis of DNA. Moreover, the RLS assay result was validated by seasoned vitro methods. The proposed RLS assay is not only an unprecedented one for primarily determine the binding mode of oridonin to DNA, but also a simple, sensitive, objective and straightforward method for the detection of ORI.

A novel probe density controllable electrochemiluminescence biosensor for ultra-sensitive detection of Hg2+ based on DNA hybridization optimization with gold nanoparticles array patterned self-assembly platform.

Biosensor based on DNA hybridization holds great potential to get higher sensitivity as the optimal DNA hybridization efficiency can be achieved by controlling the distribution and orientation of probe strands on the transducer surface. In this work, an innovative strategy is reported to tap the sensitivity potential of current electrochemiluminescence (ECL) biosensing system by dispersedly anchoring the DNA beacons on the gold nanoparticles (GNPs) array which was electrodeposited on the glassy carbon electrode surface, rather than simply sprawling the coil-like strands onto planar gold surface. The strategy was developed by designing a "signal-on" ECL biosensing switch fabricated on the GNPs nanopatterned electrode surface for enhanced ultra-sensitivity detection of Hg(2+). A 57-mer hairpin-DNA labeled with ferrocene as ECL quencher and a 13-mer DNA labeled with Ru(bpy)3(2+) as reporter were hybridized to construct the signal generator in off-state. A 31-mer thymine (T)-rich capture-DNA was introduced to form T-T mismatches with the loop sequence of the hairpin-DNA in the presence of Hg(2+) and induce the stem-loop open, meanwhile the ECL "signal-on" was triggered. The peak sensitivity with the lowest detection limit of 0.1 nM was achieved with the optimal GNPs number density while exorbitant GNPs deposition resulted in sensitivity deterioration for the biosensor. We expect the present strategy could lead the renovation of the existing probe-immobilized ECL genosensor design to get an even higher sensitivity in ultralow level of target detection such as the identification of genetic diseases and disorders in basic research and clinical application.

A fluorescence switch sensor for 6-mercaptopurine detection based on gold nanoparticles stabilized by biomacromolecule.

It is of great significance to develop a simple and powerful assay of 6-mercaptopurine (6-MP) because of its serious side effect and variable activity with the plasma concentration. In this contribution, a fluorescence switch sensor for trace amount detection of 6-MP was successfully developed based on the fluorescent gold nanoparticles stabilized by macromolecules. With the turn-off and on of the fluorescence signal at 640 nm of the analytical system, the selectivity of the present assay was largely improved. Trace amount of 6-MP could be detected in the linear range 1.0×10(-7) M-1.2×10(-4) M with a detection limit 1.98×10(-8) M. Under a UV lamp, the color change with the variation of the 6-MP concentration could be seen clearly by naked eyes. The sensitivity and selectivity are several-fold greater than other methods. And also it proved to be able to detect trace amount of 6-MP in real samples. The present assay largely improved the application of spectral methods in quantitative analysis of 6-MP.

A novel electrochemiluminescence ethanol biosensor based on tris(2,2'-bipyridine) ruthenium (II) and alcohol dehydrogenase immobilized in graphene/bovine serum albumin composite film.

We developed a novel electrochemiluminescence (ECL) ethanol biosensor based on Ru(bpy)(3)(2+) and alcohol dehydrogenase (ADH) immobilized by graphene/bovine serum albumin composite film. The graphene film was directly formed on a glassy carbon electrode surface via an in situ reduction of graphene oxide (GO) and Ru(bpy)(3)(2+) was immobilized during its formation. The graphene film acted as both a decorating agent for immobilization of Ru(bpy)(3)(2+) and a matrix to immobilize bovine serum albumin (BSA), meanwhile BSA not only acted as a reductant to reduce GO, but also provided a friendly environment for ADH immobilization. Furthermore, ADH was separated from Ru(bpy)(3)(2+) by the electron-conductive graphene/BSA composite film to retain its enzymatic activity. The experimental results indicated that the biosensor had excellent electrochemical activity, ECL response to ethanol and stability. Such a design of Ru(bpy)(3)(2+)-graphene/BSA film to modify electrode holds a great promise as a new biocompatible platform for the development of enzyme-based ECL biosensors.

Functionalized gold nanorods as an immunosensor probe for neuron specific enolase sensing via resonance light scattering.

A novel resonance light scattering assay for neuron specific enolase (NSE) with high selectivity and sensitivity has been developed by using functionalized gold nanorods as an immunosensor probe.

A highly sensitive label-free resonance light scattering assay of carcinoembryonic antigen based on immune complexes.

As a kind of glycoprotein, carcinoembryonic antigen (CEA) is the important tumor marker for clinical diagnosis of the presence or recurrence of cancer. In this work, a novel label-free resonance light scattering (RLS) spectral CEA assay was developed based on the combination of highly selective immunoreaction and ultrasensitive RLS technique. In Tris-HCl buffer solution (pH 7.5), the specific immunoreaction between CEA antigen and mouse anti-CEA formed immune complexes which had a maximum RLS spectral peak at 389.0 nm, with the existence of physiological saline and polyethylene glycol 20,000 (PEG 20,000). Under the optimal conditions, the magnitude of enhanced RLS intensity (ΔI(RLS)) was proportional to the concentration of CEA in the range from 0.1 to 60 ng mL(-1), with a detection limit (LOD, 3σ) of 0.03 ng mL(-1). The characteristics of RLS, the CEA immunocomplex, the immune response, the ratio of CEA antigen and mouse anti-CEA, and the optimum conditions of the immunoreaction have been investigated. The CEA concentrations of 20 serum specimens detected by the developed assay showed consistent results in comparison with those obtained by commercially available enzyme-linked immunosorbent assay (ELISA) kit. And this method has many satisfying merits including label-free, sensitivity and high selectivity.

Label-free fluorescence turn on detection of tiopronin with tunable dynamic range based on the ensemble of Alizarin Red S/copper ion.

In this study, a new type of rapid, label-free fluorescence turn-on assay for detection of tiopronin using Alizarin Red S (ARS)/copper ion ensemble is developed. ARS is high fluorescence in BR buffer solution. But, the fluorescence of ARS can be significantly quenched by copper ions due to ground-state complexation. However, in the presence of tiopronin, copper ions were released from the ARS and thus restored the fluorescence of ARS. The assay has several important features. First, the system is simple in design, fast in operation and is more convenient and promising than other methods. Second, the proposed assay eliminated the separation process and sophisticated instrumentations. Third, the detection process can be seen with the naked eye and can be easily adapted to automated high-throughput screening. At last, the assay has high sensitivity and selectivity for tiopronin and the detection limit is 0.8 ng/mL which is lower than or at least comparable to the previous methods. Moreover, the dynamic range of the sensor can be tuned simply by adjusting the concentration of copper ions. Importantly, the protocol offers high selectivity for the determination of tiopronin in pharmaceutical tablets, injection and biological samples with satisfactory results. Thus, the assay shows great potential applications in the fields of pharmaceuticals and clinical analysis.

Preparation of cyano-functionalized multiwalled carbon nanotubes as solid-phase extraction sorbent for preconcentration of phenolic compounds in environmental water.

In the present work, we showed a novel method to synthesize cyano-functionalized multiwalled carbon nanotubes (MWCNTs-CN) and utilize it as a solid-phase extraction sorbent for preconcentration of phenolic compounds in environmental water samples. MWCNTs-CN was synthesized through surface functionalization of multiwalled carbon nanotubes (MWCNTs). The functional groups on the surface of modified MWCNTs were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. The analytical procedure was based on a conventional solid-phase extraction step for which 100 mg of MWCNTs-CN were packed in a 3 mL polypropylene cartridge. Analytes were thus isolated and preconcentrated from the pretreated samples and subsequently detected on high-performance liquid chromatography-ultraviolet detection. The results showed the proposed method exhibited good sensitivity and precision for the extraction and elution of analytes. The limit of detections (S/N = 3) of the method were 0.45, 0.09, 0.08, and 3.00 ng mL(-1) for p-chlorophenol, 1-naphthol, 2-naphthol, and 2,4-dichlorophenol, respectively. The mean relative recoveries (n = 3) were between 80.28 and 103.13%, and the repeatability (RSD ≤ 5.10%) and reproducibility (RSD ≤ 7.68%) were accepted. This developed method was applied to determine phenolic compounds in environmental water samples. There is a positive result only for 2-naphthol with concentration of 0.38 ng mL(-1) in seawater sample.

A resonance light scattering sensor based on methylene blue-sodium dodecyl benzene sulfonate for ultrasensitive detection of guanine base associated mutations.

A resonance light scattering (RLS) sensor for guanine base associated mutations has been developed on the basis of the high selectivity of methylene blue (MB) for guanine bases in the presence of sodium dodecyl benzene sulfonate (SDBS). MB, when bound to SDBS, underwent a dramatic enhancement of its RLS intensity. However, the addition of double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) caused the strong RLS intensity of MB-SDBS to decrease, and the RLS intensity of MB-SDBS-ssDNA was much lower than that of MB-SDBS-dsDNA. Consequently, it can be concluded that the binding abilities of MB-SDBS with ssDNA and dsDNA were different. Besides, the experimental results showed that MB-SDBS could bind specifically to oligonucleotides rich in guanine bases. Short DNA targets with sequences related to ß-thalassaemia, thrombophilia and psoriasis, all of which are guanine base relevant mutations, were synthesized. It was found that MB-SDBS could recognize the single-base mismatches in the mutational DNA, followed by different RLS signal changes between MB-SDBS-normal DNA systems and MB-SDBS-mutational DNA systems. The ultrasensitive sensor allows simple, rapid, sensitive and selective detection of guanine base associated mutations, indicating its potential application in the medical field.

Protein-templated gold nanoclusters as fluorescence probes for the detection of methotrexate.

In this contribution, bovine serum albumin stabilized gold nanoclusters as novel fluorescent probes were successfully utilized for the detection of methotrexate for the first time. Our prepared gold nanoclusters exhibited strong emission with peak maximum at 633.5 nm. However, the addition of methotrexate induced the strong fluorescence intensity of the gold nanoclusters to decrease. The decrease in fluorescence intensity of the gold nanoclusters caused by methotrexate allowed the sensitive detection of methotrexate in the range of 0.0016 µg mL(-1) to 24 µg mL(-1). The detection limit for methotrexate is 0.9 ng mL(-1) at a signal-to-noise ratio of 3. The present sensor for methotrexate detection possessed a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.

A label-free method for studying DNA sequence recognition of mitoxantrone based on resonance light-scattering technique.

A label-free method for studying DNA sequence recognition of mitoxantrone (MIT) by resonance light-scattering (RLS) technique has been developed in this contribution. Through the RLS spectra, the selective no-covalent interactions between MIT and double-stranded DNA, single-stranded DNA (ssDNA), oligonucleotides were systematically studied. The results of the experiments displayed that MIT had an obvious preference to ssDNA with the K (K(RLS)), 15.16 mmol mg(-1) and the number of binding sites (N), 8.68 × 10(-4) mmol mg(-1). Besides, it was found that MIT had a preference to sequences that were rich in guanine and cytosine bases with K(RLS), 17.29 l mmol(-1) and N, 1.19 × 10(-2) l mmol(-1). The recognition mechanisms were well discussed and by fluorescence method and atom force microscopy, the RLS technique was confirmed to be a reliable method in this study. Compared with other methods, what the RLS strategy displayed was the direct interaction between anticancer drugs and DNA in vitro without the influence of a foreign substance. Thus, it can be a simple, fast and label-free strategy for DNA sequence recognition studies of DNA-targeted anticancer drugs.

Alizarin red S/copper ion-based ensemble for fluorescence turn on detection of glutathione with tunable dynamic range.

In this study, a new type of rapid, high sensitive and selective fluorescence turn-on assay for detection of glutathione using an Alizarin Red S/copper ion ensemble is developed. This assay is based on the highly specific interaction between the glutathione and the copper ions and the strong fluorescence Alizarin Red S probe in a competition assay format. The system is simple in design, fast in operation and is more convenient and promising than other methods. The novel strategy eliminated the separation process, chemical modifications, and sophisticated instrumentations. The detection and discrimination process can be seen with the naked eye and can be easily adapted to automated high-throughput screening. The assay has high sensitivity and selectivity for glutathione. The detection limit is 2.3 nM, it is lower than or at least comparable to previous methods. The dynamic range of the sensor can be tuned simply by adjusting the concentration of copper ions. Importantly, the protocol offers high selectivity for the determination of glutathione among amino acids found in proteins, as well as in serum samples. The assay shows great potential for practical application as a disease-associated biomarker and it will be needed to satisfy the great demand of amino acid determination in the fields such as biochemistry, pharmaceuticals, and clinical analysis.

Sensitive and selective detection of glutathione based on resonance light scattering using sensitive gold nanoparticles as colorimetric probes.

In this paper, we reported the development of a highly sensitive and selective resonance light scattering (RLS) technique for glutathione using gold nanoparticle probes. The assay relies upon the distance-dependent optical properties of gold nanoparticles, the self-assembly of glutathione on gold nanoparticles, and the interaction of a 2 : 1 glutathione-Cu(2+) complex. In the presence of Cu(2+), glutathione could rapidly induce the aggregation of gold nanoparticles, thereby resulting in greatly enhanced RLS intensity and red-to-blue (or purple) color change. The concentration of glutathione can be determined by the naked eye or a fluorescence spectrometer. Under the optical conditions, the detection of glutathione can be finished within 20 min, and the detection limit of 10 nM can be reached. The concentration range of the probe is 40-280 nM. The proposed method holds a specific selectivity toward glutathione and it is applied to the detection of glutathione in human serum with satisfactory results. In addition, the assay shows great potential application for disease-associated biomarkers, and it will meet the great demand for amino acid determination in fields such as food processing, biochemistry, pharmaceutical, and clinical analysis.

An aptamer based resonance light scattering assay of prostate specific antigen.

Prostate specific antigen (PSA) is a valuable tumor marker for prostate cancer screening. In this work, a novel and sensitive resonance light scattering (RLS) spectral assay of PSA was proposed based on PSA aptamer modified gold nanoparticles (AuNPs). The sulfhydryl modified single-strand aptamer could interact with AuNPs, which made the AuNPs stable in high concentration of salt. In pH 7.0 BR buffer solution, the highly selective combination of PSA and AuNPs-labeling aptamer resulted in the aggregation of AuNPs which showed high RLS intensity. Under the optimal conditions, the magnitude of enhanced RLS intensity (ΔI(RLS)) was proportional to the concentration of PSA in the range from 0.13 to 110 ng/mL, with a detection limit (LOD, 3σ) of 0.032 ng/mL. This developed RLS assay as well as a commercially available enzyme-linked immunosorbent assay (ELISA) kit was successfully applied to the detection of PSA in 15 serum samples, and an excellent correlation of the levels of PSA measured was obtained. This is the first report of the aptamer based RLS assay for PSA and it is also a significant application of instrumental analysis technique.

Protein-templated gold nanoclusters based sensor for off-on detection of ciprofloxacin with a high selectivity.

In this contribution, bovine serum albumin stabilized gold nanoclusters as novel fluorescent probes were successfully utilized for the detection of ciprofloxacin for the first time. Our prepared gold nanoclusters exhibited strong emission with peak maximum at 635 nm. Cu(2+) was employed to quench the strong fluorescence of the gold nanoclusters, whereas the addition of ciprofloxacin caused the fluorescence intensity restoration of the Cu(2+)-gold nanoclusters system. The increase in fluorescence intensity of Cu(2+)-gold nanoclusters system caused by ciprofloxacin allows the sensitive detection of ciprofloxacin in the range of 0.4 ng mL(-1) to 50 ng mL(-1). The detection limit for ciprofloxacin is 0.3 ng mL(-1) at a signal-to-noise ratio of 3. The present sensor for ciprofloxacin detection possesses a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.

A resonance light-scattering off-on system for studies of the selective interaction between adriamycin and DNA.

On the basis of the resonance light scattering (RLS) of Ag nanoparticles (AgNPs), an RLS off-on system was developed for studies of the selective interaction between adriamycin (ADM) and DNA. In this strategy, addition of ADM could induce a proportional decrease in the RLS intensity of AgNPs; this could be used to detect trace amounts of ADM with a detection limit of 12.75 ng mL(-1) in the range 0.021-10.0 µg mL(-1). Subsequently, by investigating the ability of different DNA sequences to restore the RLS intensity of the analytical systems, we found that ADM was selective to dsDNA and had an obvious preference for sequences that were rich in guanine and cytosine bases. In order to validate the results of the RLS assay, fluorescence quenching was used, and binding constants and binding numbers of each system were calculated. Compared with other methods, this RLS off-on strategy was more sensitive, fast, and reliable. It has also supplied a novel method for studying the sequence selectivity of DNA-targeted anticancer drugs and is a novel application of the RLS technique in analytical chemistry.

A resonance light scattering quenching system for studying DNA sequence recognition of actinomycin D.

The DNA sequence recognition study of DNA-targeted anticancer drugs is a theoretical basis for improving the selectivity of anticancer drugs. With the high synergy effect of cocoamidopropyl hydroxy sulfobetaine (HSB), a resonance light scattering (RLS) quenching system for DNA sequence recognition studies of actinomycin D (ACTD) was developed in this contribution. By the strategy, DNA sequence selectivity as well as the recognition mechanisms of ACTD was systematically investigated. The results suggested that ACTD had the selectivity to single-stranded DNA (ssDNA) with an equilibrium constant (K(RLS)) of 12.4 mmol mg(-1). Also it had a preference for Guanine and Cytosine bases with a K(RLS) of 6.69 L mmol(-1). The selectivity mechanism between ACTD and DNA was also well discussed with the help of UV-Vis absorption spectroscopy. Compared with other methods, the RLS quenching system has the advantages of reliability and speediness, and it avoids complex modification processes and is a better bionic system for the above research. Results obtained from this work would supply a theoretical basis for improving anticancer activity and designing similar anticancer drugs.

High-sensitivity determination of curcumin in human urine using gemini zwitterionic surfactant as a probe by resonance light scattering technique.

INTRODUCTION: Curcumin is a popular plant medicine that is extracted from turmeric dry rhizomes of Curcuma longa Linn. The study of curcumin is well established and is currently becoming a centre of attention. OBJECTIVE: To develop a steady and simple assay for curcumin determination at the nanogram level based on the intense resonance light scattering (RLS) enhancement due to the interaction between curcumin and phosphodiesters quaternary ammonium salt (PQAS). METHODOLOGY: PQAS, a new kind of Gemini zwitterionic surfactant, was used as the probe for the determination of curcumin by the RLS technique. A series of validation experiments was also performed. RESULTS: A linear relationship was constructed between the ΔI(RLS) and the concentration of curcumin. The linear regression equation was presented as ΔI(RLS) = 8.37 + 44.92c (µg/mL) with the regression coefficient r = 0.9987 (n = 12) and the linear range was 0.08-60.0 µg/mL. The detection limit (3σ) was 2.6 ng/mL. CONCLUSION: The proposed method can be used to detect the content of curcumin in human urine samples and this new assay using PQAS as a probe was more sensitive and displayed a wider linear range than that reported previously.

A new way to detect the interaction of DNA and anticancer drugs based on the decreased resonance light scattering signal and its potential application.

A novel assay has been developed to detect the interaction of DNA and anticancer drugs based on the decreased resonance light scattering (RLS) technique. The proposed method can be used to study those drugs which do not produce a RLS-signal after binding to DNA. RLS was used to monitor the interaction of five anticancer drugs with DNA. The reaction between anticancer drugs and DNA took place in BR buffer solution. From the RLS assay, the sequence of five anticancer drugs activities was as follows: CTX < MTX < Pt < MMC < 5-Fu. Mammary cancer cell DNA (mcDNA) was involved to validate the RLS assay. The results showed that the sensitivities of the five anticancer drugs targeting both mcDNA and ctDNA increased in the same order. However the sensitivity of each drug to mcDNA was higher than that to ctDNA It is a significant innovation of the RLS method to detect the interaction of DNA and anticancer drugs and to obtain drug sensitivity, which provides new strategies to screen DNA targeted anticancer drugs.