Surface plasmon resonance based indirect immunoassay for detection of 17ß-estradiol.

A surface plasmon resonance (SPR) based immunosensor is presented for highly sensitive and selective detection of 17ß-estradiol by the indirect competitive inhibition immuno assay, employing anti-17 ß-estradiol antibody as high molecular weight (HMW) interactant. Immobilization of estradiol-BSA conjugate onto the nano thin gold surface was accomplished by covalent amide linkage through self assembled monolayer. The proposed biosensor is simple to fabricate, reproducible and exhibit excellent sensitivity for estrogen (detection limit,1 pg mL-1) without any significant interference from structurally similar steroidal hormone, progesterone and non-steroidal compound bisphenol-A. The proposed surface displayed a high level of stability during repeated regeneration and immunoreaction cycles suitable for biosensor development.

Surface plasmon resonance based immunosensor for serological diagnosis of dengue virus infection.

Surface plasmon resonance (SPR) is a promising tool in sensor technology for biomedical applications. An SPR based immunosensor was established for label free and real time assay for the serological diagnosis of dengue virus infection employing the dengue virus antigen as the sensing element. The dengue virus antigen conjugated with bovine serum albumin is covalently immobilized on a gold sensor chip via activated self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid, by amide coupling. Surface morphology of the biosensor was recorded using atomic force microscopy. Presence of dengue virus specific IgM antibodies in dengue positive sera was monitored by increase in resonance angle in direct immunoassay, whereas the principle of indirect competitive inhibition immunoassay was used to detect presence of dengue virus for early detection of the onset of dengue viral infection in clinical diagnostics. Results were compared with those obtained by MAC-ELISA. The regeneration was achieved by pepsin solution in glycin-HCl buffer (pH 2.2) and sensor surface displayed a high level of stability during repeated immunoreaction cycles. The proposed biosensor being simple, effective and based on utilization of natural antigen-antibody affinity, our study presents an encouraging scope for development of biosensors for diagnosis of dengue and dengue hemorrhagic fever (DHF) which continues to be a major health problem in the tropical and subtropical regions of world.

Surface plasmon resonance biosensor for dopamine using D3 dopamine receptor as a biorecognition molecule.

In modern biomedical technology, development of high performance sensing methods for dopamine (DA) is a critical issue because of its vital role in human metabolism. We report here, a new kind of bioaffinity sensor for DA based on surface plasmon resonance (SPR) using a D(3) dopamine receptor (DA-RC) as a recognition element. A conjugate of DA was synthesized using bovine serum albumin (BSA) protein and was characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The biosensor surface was constructed by the immobilization of the DA-BSA conjugate onto an SPR gold surface by physical adsorption. Atomic force microscopy (AFM) investigations revealed that the DA-BSA conjugate was homogeneously distributed over the sensor surface. Specific interaction of the DA-RC with the immobilized DA-BSA conjugate was studied by SPR. Based on the principle of indirect competitive inhibition, the biosensor could detect DA in a linear dynamic range from 85 pg/ml (ppt) to 700 ng/ml (ppb). The biosensor was highly specific for DA and showed no significant interference from potent interferences such as ascorbic acid (AA), uric acid (UA) and other DA analogues viz., 3,4 dihydroxyphenyl acetic acid (DOPAC) and 3-(3,4 dihydroxyphenyl)-alanine (DOPA). The sensor surface displayed a high level of stability during repeated regeneration and affinity reaction cycles. Since this biosensor is simple, effective and is based on utilization of natural receptor, our study presents an encouraging scope for development of portable detection systems for in-vitro and in-vivo measurement of DA in clinical and medical diagnostics.

Electrochemical behaviour of isatin at a glassy carbon electrode.

The electrochemical behavior of isatin--a molecule with a broad range of applications in synthetic, biological and clinical activity--has been investigated over a wide pH range at a glassy carbon electrode (GCE) using cyclic, square wave and differential pulse voltammetry. The oxidation of isatin is an irreversible process, pH dependent and occurs with the formation of a main oxidation product that strongly adsorbs on the electrode surface. The reduction of isatin is also a pH dependent irreversible process. Cyclic voltammograms show two consecutive charge transfer reactions. The diffusion coefficient of isatin was calculated in pH 7.0 phosphate buffer to be D(0)=4.9 x 10(-7) cm2 s(-1). The limit of detection obtained in a solution of pH 7.0 phosphate buffer was LOD=0.194 microM, based on three times the noise level.