The simultaneous detection of free and total prostate antigen in serum samples with high sensitivity and specificity by using the dual-channel surface plasmon resonance.

Free/total prostate antigen (f/t-PSA) ratio in serum as a promising parameter has been used to improve the differentiation of benign and malignant prostate disease. In order to obtain the accurate and reliable f/t-PSA ratio, the simultaneous detection of f-PSA and t-PSA with high sensitivity and specificity is required. In this work, the dual-channel surface plasmon resonance (SPR) has been employed to meet the requirement. In one channel, t-PSA was directly measured with a linear range from 1.0 to 20.0 ng/mL. In another channel, due to the low concentration of f-PSA in serum, the asynchronous competitive inhibition immunoassay with f-PSA@Au nanoparticles (AuNPs) was developed. As expected, the detection sensitivity of f-PSA was greatly enhanced, and a linear correlation with wider linear range from 0.010 to 0.40 ng/mL was also achieved. On the other hand, a simple method was explored for significantly reducing the non-specific adsorption of co-existing proteins. On basis of this, the f/t-PSA ratios in serum samples from prostate cancer (PCa) or benign prostatic hyperplasia (BPH) patients were measured. And it was found that there was significant difference between the distributions of f/t-PSA ratio in BPH patients (16.44±1.77%) and those in PCa patients (24.53±4.97%). This present work provides an effective method for distinguishing PCa from BPH, which lays a potential foundation for the early diagnosis of PCa.

A reusable localized surface plasmon resonance biosensor for quantitative detection of serum squamous cell carcinoma antigen in cervical cancer patients based on silver nanoparticles array.

Squamous cell carcinoma antigen (SCCa), as a tumor biomarker, plays an important role in adjuvant diagnosis, treatment evaluation, and prognosis prediction for cervical cancer patients. Localized surface plasmon resonance (LSPR) technique based on noble metal nanoparticles bypasses the disadvantages of traditional testing strategies, in terms of free-labeling, short assay time, good sensitivity, and selectivity. Herein, we develop a novel and reusable LSPR biosensor for the detection of SCCa. First, a triangle-shaped silver nanoparticle array was fabricated using the nanosphere lithography method. Next, we investigated and verified the feasibility of amino coupling method using 11-mercaptoundecanoic acid (MUA) to form a functionalized chip surface with monoclonal anti-SCCa antibodies on the silver nanoparticles for distinct detection of SCCa. Different concentrations of SCCa were successfully tested in both buffer and human serum by the ultrasensitive and specific LSPR system, with a linear quantitative detection range of 0.1-1,000 pM under optimal conditions. With appropriate regeneration solution, for example 50 mM glycine-HCl (pH 2.0), the LSPR biosensor featured effective fabrication reproducibility, which reduced both production cost and testing time. Our study represents the first application of the LSPR biosensor in cervical cancer, and demonstrates that the rapid, simple, and reusable nanochip can serve as a potential alternative for clinical serological diagnosis of SCCa in cervical cancer patients.

Oligopeptides functionalized surface plasmon resonance biosensors for detecting thiacloprid and imidacloprid.

By using phage display library, we identified two highly specific oligopeptide sequences RKRIRRMMPRPS and RNRHTHLRTRPR for binding neonicotinoids such as thiacloprid and imidacloprid. The former shows high affinity for thiacloprid whereas the latter shows high affinity for imidacloprid. Surprisingly, cross binding is minimal despite the similarity of the two molecules. To develop a neonicotinoid biosensor, these two oligopeptides are synthesized and immobilized on the surface of a surface plasmon resonance (SPR) chip with a bare-gold surface. This oligopeptide functionalized SPR biosensor can rapidly detect thiacloprid and imidacloprid in buffer solutions in a real-time manner. The limit of detection (LOD) for thiacloprid and imidacloprid is 1.2 µM and 0.9 µM, respectively.

Surface plasmon resonance biosensor for parallelized detection of protein biomarkers in diluted blood plasma.

Surface plasmon resonance (SPR) biosensor for high-throughput screening of protein biomarkers in diluted blood plasma is reported. The biosensor combines a high-resolution SPR imaging sensor and a high-density protein array with low-fouling background. The SPR imaging sensor utilizes polarization contrast and advanced referencing and provides a total of 120 sensing areas (each 200 µm×150 µm). Antibodies are immobilized on the sensing areas via hybridization of antibody-oligonucleotide conjugates to thiolated complementary oligonucleotides microspotted on the sensor surface (DNA-directed immobilization). A low-fouling background is achieved by covalent immobilization of bovine serum albumin to carboxyl-terminated thiols filling the areas among the thiolated oligonucleotides and outside the sensing areas. The biosensor was evaluated for detection of protein biomarkers relevant to cancer diagnostics--human chorionic gonadotropin (hCG) and activated leukocyte cell adhesion molecule (ALCAM) both in buffer and in 10% blood plasma. Limits of detection as low as 45 ng/mL (ALCAM) and 100 ng/mL (hCG) were achieved in blood plasma samples.

Sub-attomole oligonucleotide and p53 cDNA determinations via a high-resolution surface plasmon resonance combined with oligonucleotide-capped gold nanoparticle signal amplification.

Oligonucleotide (ODN)-capped gold nanoparticles (Au-NPs) were used in a sandwich assay of ODN or polynucleotide by a flow injection surface plasmon resonance (SPR). A carboxylated dextran film was immobilized onto the SPR sensor surface to eliminate nonspecific adsorption of ODN-capped Au-NPs. The tandem use of signal amplification via the adlayer of the ODN-capped Au-NPs and the differential signal detection by the bicell detector on the SPR resulted in a remarkable DNA detection level. A 39-mer target at a quantity as low as 2.1 x 10(-20)mol, corresponding to 1.38 fM in a 15 microl solution, can be measured. To our knowledge, both the concentration and quantity detection levels are the lowest among all the gene analyses conducted with SPR to this point. The method is shown to be reproducible (relative standard deviation values <16%) and to possess high sequence specificity. It is also demonstrated to be viable for sequence-specific p53 cDNA analysis. The successful elimination of nonspecific adsorption of, and the signal amplification by, ODN-capped Au-NPs renders the SPR attractive for cases where the DNA concentration is extremely low and the sample availability is severely limited.

Development and validation of a biosensor-based immunoassay for progesterone in bovine milk.

We have developed a rapid automated immunoassay, using the BIACORE surface plasmon resonance (SPR) biosensor, to measure progesterone in bovine milk. The assay was designed as an inhibition assay with progesterone covalently immobilised to the carboxymethyl dextran matrix of a CM5 sensor chip. A fixed amount of monoclonal anti-progesterone antibody 39C5H7 was mixed 9:1 with the sample and the amount of free antibody was then determined using biomolecular interaction analysis (BIA) by injection of the mixture over the immobilised progesterone sensor surface. The assay was designed to cover the concentration range 0.5 to 50 ng/ml. The limit of detection (LOD) was 3.56 ng/ml. Reproducibility of the assay was very good with both intra-assay and inter-assay coefficients of variation <5%. As results become available within minutes of injection and the procedure involves fully automated instrumentation, we believe that this BIA assay for progesterone in milk could be used in-line in the milking parlour and, thus, provide an important tool for reproductive management of dairy cattle to detect heat and predict pregnancy.

Kinetic analysis of the mass transport limited interaction between the tyrosine kinase lck SH2 domain and a phosphorylated peptide studied by a new cuvette-based surface plasmon resonance instrument.

We explored the use of a newly developed cuvette-based surface plasmon resonance (SPR) instrument (IBIS) to study peptide-protein interactions. We studied the interaction between the SH2 domain of lck and a phosphotyrosine peptide EPQY*EEIPIYL which was immobilized on a sensor chip. No indications for mass transport limitation (MTL) were observed when standard kinetic approaches were used. However, addition of competing peptide during dissociation revealed a high extent of rebinding. A dissociation rate constant (k(d)) of 0.6+/-0.1 s(-1) was obtained in the presence of large amounts of peptide. A simple bimolecular binding model, applying second-order kinetics for the cuvette system, could not adequately describe the data. Fits were improved upon including a step in the model which describes diffusion of the SH2 domain from the bulk to the sensor, especially for a surface with high binding capacity. From experiments in glycerol-containing buffers, it appeared that the diffusion rate decreased with higher viscosity. It is demonstrated that MTL during association and dissociation can be described by the same diffusion rate. A binding constant (K(D)) of 5.9+/-0.8 nM was obtained from the SPR equilibrium signals by fitting to a Langmuir binding isotherm, with correction for loss of free analyte due to binding. An association rate constant k(a) of 1.1(+/-0.2)x10(8) M(-1) x s(-1) was obtained from k(d)/K(D). The values for k(a) and k(d) obtained in this way were 2-3 orders larger than that from standard kinetic analysis, ignoring MTL. We conclude that in a cuvette the extent of MTL is comparable to that in a flow system.