Gold nanoparticle-based colorimetric assay for the direct detection of cancerous cells

Early and accurate detection of cancer often requires time-consuming techniques and expensive instrumentation. To address these limitations, we developed a colorimetric assay for the direct detection of diseased cells. The assay uses aptamer-conjugated gold nanoparticles to combine the selectivity and affinity of aptamers and the spectroscopic advantages of gold nanoparticles to allow for the sensitive detection of cancer cells. Samples with the target cells present exhibited a distinct color change while nontarget samples did not elicit any change in color. The assay also showed excellent sensitivity with both the naked eye and based on absorbance measurements. In addition, the assay was able to differentiate between different types of target and control cells based on the aptamer used in the assay indicating the wide applicability of the assay for diseased cell detection. On the basis of these qualities, aptamer-conjugated gold nanoparticles could become a powerful tool for point of care diagnostics.     

A DNA-gold nanoparticle-based colorimetric competition assay for the detection of cysteine

We report the development of a highly sensitive and selective colorimetric detection method for cysteine based upon oligonucleotide-functionalized gold nanoparticle probes that contain strategically placed thymidine-thymidine (T-T) mismatches complexed with Hg2+. This assay relies upon the distance-dependent optical properties of gold nanoparticles, the sharp melting transition of oligonucleotide-linked nanoparticle aggregates, and the very selective coordination of Hg2+ with cysteine. The concentration of cysteine can be determined by monitoring with the naked eye or a UV-vis spectrometer the temperature at which the purple-to-red color change associated with aggregate dissociation takes place. This assay does not utilize organic cosolvents, enzymatic reactions, light-sensitive dye molecules, lengthy protocols, or sophisticated instrumentation thereby overcoming some of the limitations of more conventional methods.     

A facile low-cost synthesis of ZnO nanorods via a solid-state reaction at low temperature

ZnO nanorods have been prepared via a solid-state reaction between anhydrous zinc sulfate and sodium hydroxide in the absence of surfactant and template at relatively low temperature. The products were characterized by XRD, XPS and TEM. The influence of Zn²⁺/OH⁻ ratio on the size and morphology of the as-prepared ZnO samples has been studied, and the experimental results showed that when Zn²⁺/OH⁻ ratio was 1:4, good rod-like morphology with the diameter of 30–50 nm and length of ca. 600 nm can be obtained. Finally, the mechanism for the ZnO nanorods developed in the reaction system has been explained.     

A Cu@Au nanoparticle-based colorimetric competition assay for the detection of sulfide anion and cysteine

As an extension of our previous work, which described the unique ability of the core/shell Cu@Au nanoparticle (NP) to selectively recognize iodide, (1) herein, we wish to report the development of an alternatively sensitive and selective colorimetric detection for sulfide anion and cysteine based upon the Cu@Au NP by a competition avenue. In the absence of sulfide anion or cysteine, iodide can induce an appreciable color change of the Cu@Au NP solution from purple to red by transforming the clusters of NP to single, nearly spherical, and larger ones. However, the transformation is severely interfered by the presence of sulfide or cysteine because of a higher binding strength of the S-Au bond than the I-Au one. As a result, the clear purple-to-red color change induced by iodide is affected as a correlation with the concentration of sulfide or cysteine. By taking advantage of this fact, we can detect a concentration of 3 μM for sulfide and 0.4 μM for cysteine with the naked eye or 0.3 μM (10 ppb) for sulfide and 50 nM (6 ppb) for cysteine aided by a UV/vis spectrometer. Given the detrimental effect of hydrogen sulfide and the biological importance of cysteine, the assay may become useful in the environment monitoring, water quality inspection and biomedical diagnosis as well.     

A facile low temperature solvothermal route to copper monosulfide submicrotubes

The synthesis of copper monosulfide (CuS) submicrotubes under mild conditions has been achieved by two simple steps: firstly, a precursor (copper-thiosulfate complexes) was prepared through the precipitation reaction of CuSO₄·5H₂O and Na₂S₂O₃·5H₂O in distilled water at room temperature; then, in the absence of any extra catalyst, surfactant or template, pure submicrometer-sized CuS crystallites with a tubular morphology could be obtained just via solvothermal treatment of the precursor in ethanol at 150-180 °C for 12-24 h. Also, the effects of the reaction temperature and reaction time on the phase and morphology of the resultant products were investigated and the possible formation mechanism of tubular structure CuS crystallites in this solvothermal system was discussed.     

Development of an electrochemical immunosensor for direct detection of interferon-gamma at the attomolar level

An electrochemical immunosensor for direct detection of the 15.5-kDa protein interferon-gamma (IFN-gamma) at attomolar level has been developed. Self-assembled monolayers (SAMs) of cysteine or acetylcysteine are formed on electropolished polycrystalline Au electrodes. IFN-gamma adsorbs physically to each of these SAMs. With injections of 100 mM KCl, IFN-gamma can be removed in the flow without damaging the acetylcysteine SAM. However, the cysteine SAM is affected by these KCl injections. In an on-line procedure in the flow, a specific antibody (MD-2) against IFN-gamma is covalently attached following carbodiimide/succinimide activation of the SAM. The activation of the carboxylic groups, attachment of MD-2, and deactivation of the remaining succinimide groups with ethanolamine are monitored impedimetrically at a frequency of 113 Hz, a potential of +0.2 V versus SCE, and an ac modulation amplitude of 10 mV. Plots of the real (Z') and imaginary (Z") component of the impedance versus time provide the information to control these processes. In the thermostated setup (23.0 degrees C), samples of unlabeled IFN-gamma (in phosphate buffer pH 7.4) are injected and the binding with immobilized MD-2 is monitored with ac impedance or potential-step methods. While the chronoamperometric results are rather poor, the ac impedance approach provides unsurpassed detection limits, as low as 0.02 fg mL-1 (approximately 1 aM) IFN-gamma. From a calibration curve (i.e. Z" versus the amount injected), recorded by multiple 50-microL injections of 2 pg mL(-1) of IFN-gamma, a dynamic range of 0-12 pg mL(-1) could be derived. However, when nonspecific adsorption is taken into account, which has been found to be largely reduced through injections of 100 mM KCl, a much smaller dynamic range of 0-0.14 fg mL(-1) remains. The immunosensor can be regenerated by using a sequence of potential pulses in the flow by which the SAM with attached MD-2 and bound IFN-gamma is completely removed. When the developed procedures described above are repeated, the response of the immunosensor is reproducible within 10%.     

Enzymatic cleavage of nucleic acids on gold nanoparticles: a generic platform for facile colorimetric biosensors

The enzymatic cleavage of nucleic acids (DNA or DNA with a single RNA linkage) on well-dispersed gold nanoparticles (AuNPs) is exploited in the design of facile colorimetric biosensors. The assays are performed at salt concentrations such that DNA-modified AuNPs are barely stabilized by the electrostatic and steric stabilization. Enzymatic cleavage of DNA chains on the AuNP surface destabilizes the AuNPs, resulting in a rapid aggregation driven by van der Waals attraction, and a red-to-purple color change. Two different systems are chosen, DNase I (a DNA endonuclease) and 8-17 (a Pb(2+)-depedent RNA-cleaving DNAzyme), to demonstrate the utility of our assay for the detection of metal ions and sensing enzyme activities. Compared with previous studies in which AuNP aggregates are converted into dispersed AuNPs by enzymatic cleavage of DNA crosslinkers, the present assay is technically simpler. Moreover, the accessibility of DNA to biomolecular recognition elements (e.g. enzymes) on well-dispersed AuNPs in our assay appears to be higher than that embedded inside aggregates. This biosensing system should be readily adaptable to other enzymes or substrates for detection of analytes such as small molecules, proteases and their inhibitors.     

Core/shell Cu@Ag nanoparticle: a versatile platform for colorimetric visualization of inorganic anions

Recognition and sensing of anions in aqueous media have been of considerable interest while remaining a challenging task up to date. In this document, we wish to present a simple yet sensitive method to detect inorganic anions by colorimetry based on the citrate-stabilized core/shell Cu@Ag nanoparticle (NP). It was found that the NP could discriminate some specific anions (Cl(-), Br(-), I(-), S(2-), and SCN(-)) from a wide range of environmentally dominant anions (F(-), SO(4)(2-), H(2)PO(4)(-), CO(3)(2-), NO(3)(-), etc), identified by the change in the color of the buffered NP solution or the surface plasmon resonance (SPR) absorbance band in the UV-vis spectrum. Among the recognized anions, four types of variation in the SPR absorption band were revealed. It was strongly enhanced for Cl(-) and Br(-) and was strongly damped for S(2-). For I(-), it first was slightly enhanced at lower concentrations and then gradually was damped at higher concentrations. For SCN(-), it first was slightly damped at lower concentrations and then was strongly enhanced at higher concentrations. In response to the optical change, the color of the NP solution turned from brown to bright yellow for Cl(-) (1 mM), Br(-) (10 μM), and SCN(-) (50 μM) to brownish orange for I(-) (10 μM) and to reddish orange for S(2-) (50 μM). The reason for these phenomena was postulated by the evidence of transmission electron microscope (TEM) images, X-ray photoelectron spectroscopy (XPS), and zeta potentials. In view of the importance of anions in the environment and for human health, the Cu@Ag NP colorimetric platform may have some applications, such as discriminating household table salt (NaCl) from industrial salt (NaNO(2)), testing the quality and extent of a variety of waters, and so forth.     

A facile low temperature hydrothermal route to CdSO4 nanotubes/rods

Cadmium sulphate nanotubes/rods have been synthesized by hydrothermal treatment using CdSO₄ powder as precursor and hexadecylamine (HDA) as surfactant at 180 °C for 7 days. The powder X-ray diffraction (PXRD) pattern reveals that the CdSO₄ nanotubes/rods are of orthorhombic phase. Fourier transform infrared (FTIR) spectrum shows characteristic bands due to the sulfate ion in 1114 cm^? 1 and 617 cm^? 1 region, besides bands due to the amine moiety. Transmission electron micrograph (TEM) images reveal the nanorods are of 10–15 nm in thickness and nanotubes of wall thickness 5–8 nm. UV–visible absorption spectrum of CdSO₄ nanotubes/rods shows the peak at 221 nm. Photoluminescence (PL) spectrum exhibits an intense UV band at 372 nm and weak green band at 484 nm.     

电流对小功率红光LED色度学特性的影响

本文通过改变小功率红光LED的正向驱动电流,对其光谱,色品坐标,红色比等色度学参数测试,并对半高宽,主波长,色纯度进行了计算.实验表明,这些色度学参数与电流有着密切关系.红光LED随着正向电流增加光谱产生红移,色品坐标随之变化;峰值波长与主波长向长波移动;对色纯度影响不明显,红色比略有下降.     

Detection of possible economically motivated adulterants in heparin sodium and low molecular weight heparins with a colorimetric microplate based assay

Recently, we described a 96-well plate format assay for visual detection of oversulfated chondroitin sulfate A (OSCS) contamination in heparin samples based on a water-soluble cationic polythiophene polymer (3-(2-(N-(N'-methylimidazole))ethoxy)-4-methylthiophene (LPTP)) and heparinase digestion of heparin. Here, we establish the specificity of the LPTP/heparinase test with a unique set of reagents that define the structural requirements for significant LPTP chemosensor color change. For example, we observed a biphasic behavior of larger shifts to the red in the UV absorbance spectra with decreasing average molecular weight of heparin chains with a break below 12-mer chain lengths. In addition, the oversulfation of chondroitin sulfate A (CSA) to a partially (PSCS) or fully (OSCS) sulfated form caused progressively less red shift of LPTP solutions. Furthermore, glycosaminoglycans (GAGs) containing glucuronic acid caused distinct spectral patterns compared to iduronic acid containing GAGs. We applied the LPTP/heparinase test to detection of OSCS (≥0.03% (w/w) visually or 0.01% using a plate reader) in 10 μg amounts of low molecular weight heparins (LMWHs; i.e. dalteparin, tinzaparin, or enoxaparin). Furthermore, because other oversulfated GAGs are possible economically motivated adulterants (EMAs) in heparin sodium, we tested the capacity of the LPTP/heparinase assay to detect oversulfated dermatan sulfate (OSDS), heparin (OSH), and heparan sulfate (OSHS). These potential EMAs were visually detectable at a level of ～0.1% when spiked into heparin sodium. We conclude that the LPTP/heparinase test visually detects oversulfated GAGs in heparin sodium and LMWHs in a format potentially amenable to high-throughput screening.     

A three-layer competition-based giant magnetoresistive assay for direct quantification of endoglin from human urine

This study presents a three-layer competition-based assay for ultrasensitive detection and quantification of endoglin from unprocessed human urine samples using a giant magnetoresistive (GMR) sensor and high-moment magnetic nanoparticle-based biosensing technology. This biosensing platform detects as few as 1000 copies of endoglin at concentrations as low as 83 fM with high detection specificity and has a three-order dynamic range. The results reveal that endoglin levels in urine have the potential to predict for the presence of prostate cancer and to distinguish between prostate cancers of different grades.     

Development of a low density colorimetric protein array for cardiac troponin I detection

This work presented a rapid, inexpensive, reliable, and flexible quantitative immunoassay for cardiac troponin I (cTnI). The assay was based on the concepts of one-step dual monoclonal antibody "sandwich" principle, the low density protein array, the nanogold probe, and the silver enhancement on the gold particles. The capture antibody (IgG1) coated supporting nitrocellulose membrane and the colloidal gold-labeled detection antibody (cAu-IgG2) were prepared before the detection. The detection procedure involved two steps, i.e., immunoreaction and silver amplification. The assay needs only small amounts of serum samples of patients, The whole detection procedure of the assay could be fulfilled within 40 min (much faster than the routine enzyme-linked immunosorbent assay (ELISA) that takes usually at least 3 hours for a turnaround test). The detection results could be easily imaged with a simple flatbed scanner or even observed with the naked eye. The assay showed good specific response to cTnI with very little cross-reactivity to the skeletal isoforms of troponin I (sTnl), cardiac troponin T (cTnT), and myoglobin (Mb). A cut-off value of 0.3 ng/ml was obtained from a reference control group (200 normal serum samples). 588 patients' serum samples were assayed simultaneously by routine ELISA and this colloidal gold method to test the validity of the method. The data were analyzed using the statistical package SPSS version 11.0 (SPSS Inc.) There was no significant difference between these two assays (P = 0.66 > 0.05). The agreement between this method (> or < 0.3 ng/ml) and ELISA was 86%.     

A facile approach to fabricate Ni inverse opals at controlled thickness

A vertical electrophoretic deposition method was employed to fabricate polystyrene (PS) colloidal crystals with negligible defects and considerable surface uniformity. Subsequently, the interstitial voids within the colloidal crystals were electroplated with Ni, followed by selective removal of the PS microspheres. With careful adjustment in the processing parameters, we were able to obtain Ni inverse opals at predetermined thickness in relatively short time. The inverse opals revealed superb structural stability and surface uniformity. Because the electrophoresis and electrodeposition were both carried out in a solution state, this fabrication scheme enables facile construction of inverse opals on conductive substrates over conventional approaches.     

Fracture energy of UHP-FRC under direct tensile loading applied at low strain rates

This research investigates the fracture energy of ultra-high performance fiber reinforced concretes (UHP-FRC) under direct tensile loading applied at relatively low strain rates. Nine UHP-FRC series incorporating three types of steel fibers (straight, end-hooked, and twisted fibers), each in three different fiber volume fractions, are tested under uniaxial tensile loading at four different strain rates, ranging from 0.0001 s⁻¹ to 0.1 s⁻¹. Particular attention is given to clearly distinguish between the dissipated energy during the strain hardening and softening portions of the loading regime. The test results show that: 1) the fracture energy is mainly influenced by a parameter, termed fiber factor, which is a function of the fiber volume fraction and slenderness, and 2) all three types of UHP-FRCs exhibit increases in fracture energy with increasing strain rates. The observed strain rate sensitivity of the fracture energy suggests it is likely associated with the strain sensitive micro-cracking that occurs during fiber pull-out.     

A direct and facile synthetic route for micron-scale gold prisms and fabrication of gold prism thin films on solid substrates

Flat gold prisms that have micrometer-scale edge length and nanometer-scale thickness (micro-prisms, as defined by edge length of prisms) were synthesized through a facile solution-phase synthetic method. Two effective measures were adopted in order to prepare the well-defined micro-prisms: (i) selecting poly(N-vinylpyrrolidone)(PVP) as the shape-directing agent to induce the preferential growth of small gold nanocrystals and (ii) using a weak reducing agent, ethylene glycol (EG), to slow down the reduction rate of AuCl₄^? ions. Besides, the light played an important role in inducing the formation of tiny nanoprisms in the early stages of Au(III) ion reduction. Considering that gold nanoclusters have a strong tendency to heterogeneous nucleation at solid/liquid interfaces followed by the preferential planar growth, gold prism thin films were thus fabricated on glass substrates.