Nanobiocomposite platform based on polyaniline-iron oxide-carbon nanotubes for bacterial detection.

The nanocomposite based on polyaniline (PANI)-iron oxide nanoparticles (nFe(3)O(4)) and multi walled carbon-nanotubes (CNT) has been fabricated onto indium tin oxide (ITO) coated glass plate via facile electrochemical synthesis of polyaniline in presence of nFe(3)O(4) (~20 nm) and CNT (20-80 nm in diameter). The results of transmission electron microscopic studies show evidence of coating of PANI and nFe(3)O(4) onto the CNT. The PANI-nFe(3)O(4)-CNT/ITO nanoelectrode has been characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy studies. The biotinylated nucleic acid probe sequence consisting of 20 bases has been immobilized onto PANI-nFe(3)O(4)-CNT/ITO nanoelectrode using biotin-avidin coupling. It is shown that the PANI-nFe(3)O(4)-CNT platform based biosensor can be used to specifically detect bacteria (N. gonorrhoeae) at minute concentration as low as (1×10(-19) M) indicating high sensitivity within 45 s of hybridization time at 298 K by differential pulse voltammetry using methylene blue as electroactive indicator. This bacterial sensor has also been tested with 4 positive and 4 negative PCR amplicons of gonorrhoea affected patient samples. The results of these studies have implications towards the fabrication of a handheld device for Neisseria gonorrhoeae detection that may perhaps result in a decrease in the human immunodeficiency virus infections.

DNA biosensor for detection of Neisseria gonorrhoeae causing sexually transmitted disease.

A sequence-specific electrochemical sexually transmitted disease (STD) sensor based on self-assembled monolayer of thiolated DNA probe specific to target opa gene for detection of Gonorrhoea, a sexually transmitted disease has been fabricated. 6-Mercapto-1-hexanol (MCH) has been used as a blocking agent to facilitate oligos "stand" up at the surface, a configuration favoring subsequent DNA hybridization and to repel non-specific adsorption of undesired DNA. The results of differential pulse voltammetric studies of this STD sensor reveal low detection limit (1.0 × 10(-18)M) and a wide dynamic range (from 1.0 × 10(-6)M to 0.5 × 10(-18)M) arising due to the stable hybridization using methylene blue as an electro-active DNA hybridization indicator. The experimental results with genomic DNA, clinical patient sample of Neisseria gonorrhoeae, culture of non-N. gonorrhoeae Neisseria species (NgNS) and gram negative bacteria indicate that the fabricated sensor is specific to this STD.

An amperomertic uric acid biosensor based on immobilization of uricase onto polyaniline-multiwalled carbon nanotube composite film.

A highly sensitive, amperometric uric acid biosensor possessing unique physical, electro-conductive properties of carbon nanotubes is described for determination of uric acid level in serum. A uric acid biosensor was constructed after immobilization of uricase onto a polyaniline/CNT matrix by carbonamide linkage. The scanning electron micrographs confirmed the immobilization of globular enzyme onto the electroploymerized polyaniline/CNT composite. Employment of carbon nanotubes composite in the present electrode leads to a very quick response time of 8 sec with the minimum detection limit of 5 microM along with an increase in shelf-life of electrode system to >180 days with slight loss of enzyme activity. Efficiency of the present amperometric uric acid biosensor was validated by quantitative estimation of uric acid level in biological serum of healthy individuals and the persons suffering from hyperuricemia and gout.

Polyaniline-cerium oxide nanocomposite for hydrogen peroxide sensor.

Hydrogen peroxide (H2O2) sensor has been fabricated by immobilizing horse radish peroxidase (HRP) onto polyaniline(PANI)-cerium oxide (CeO2) nano-composite film onto indium-tin-oxide (ITO) coated glass substrate using electrochemical technique. The HRP/PANI-CeO2/ITO bioelectrode has been characterized using scanning electron microscopy (SEM), Fourier Transform Infrared spectroscopy, UV-visible spectroscopy and electrochemical analysis, respectively. This electrode shows improved sensitivity (159.6 nA/mM) and detection limit (50 mM). Further this H2O2 sensor shows high HRP affinity to the PANI-CeO2 matrix as indicated by low value (2.9) mM of Michaelis-Menten constant (K(m)). This bioelectrode exhibits maximum response current at pH 7.0 and retains 90% of its initial response current after about 8 weeks.

Low density lipoprotein detection based on antibody immobilized self-assembled monolayer: investigations of kinetic and thermodynamic properties.

Human plasma low density lipoprotein (LDL) immunosensor based on surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) was fabricated by immobilizing antiapolipoprotein B (AAB) onto self-assembled monolayer (SAM) of 4-aminothiophenol (ATP). The AAB/ATP/Au immunosensor can detect LDL up to 0.252 microM (84 mg/dL) and 0.360 microM (120 mg/dL) with QCM and SPR, respectively. The SPR and QCM measurements were further utilized to study the reaction kinetics of the AAB-LDL interaction. The adsorption process involved was explored using Langmuir adsorption isotherm and Freundlich adsorption models. The thermodynamic parameters such as change in Gibb's free energy (DeltaG(ads)), change in enthalpy (DeltaH(ads)), and change in entropy (DeltaS(ads)) determined at 283, 298, and 308 K revealed that the AAB-LDL interaction is endothermic in nature and is governed by entropy. Kinetic, thermodynamic, and sticking probability studies disclosed that desorption of the water molecules from the active sites of AAB and LDL plays a key role in the interaction process and increase in temperature favors binding of LDL with the AAB/ATP/Au immunosensor. Thus, the studies were utilized to unravel the most important subprocess involved in the adsorption of LDL onto AAB-modified ATP/Au surface that may help in the fabrication of LDL immunosensors with better efficiency.

Sol-gel derived nano-structured zinc oxide film for sexually transmitted disease sensor.

A 20-mer thiolated oligonucleotide probe (th-ssDNA) specific to Neisseria gonorrhoeae immobilized onto a sol-gel derived nano-structured zinc oxide (ZnO) film dip-coated onto an indium-tin-oxide (ITO) glass substrate has been used for the fabrication of a DNA biosensor for sexually transmitted disease (gonorrhoea) detection using hybridization technique. The results of characterization studies carried out on this th-ssDNA-ZnO/ITO bioelectrode using X-ray diffraction, UV-Visible, Fourier-transform infrared, scanning electron microscopy and electrochemical techniques reveal the linearity as 0.000524 fmol-0.524 nmol, with a detection limit of 0.000704 fmol within 60 s.

STD sensor based on nucleic acid functionalized nanostructured polyaniline.

STD (sexually transmitted disease, Gonorrhoea) sensor based on nucleic acid probe (from Opa, a multi-copy gene of Neisseria gonorrhoeae) functionalized nanostructured-polyaniline coated onto indium-tin-oxide-coated glass plate has been fabricated using avidin-biotin as cross-linking agent. This DNA functionalized electrode can specifically detect upto 0.5 x 10(-15)M of complementary target within 60s of hybridization time at 25 degrees C by differential pulse voltammetry (DPV) using methylene blue as electro-active DNA hybridization indicator. This highly sensitive and specific nucleic acid functionalized nanostructured-polyaniline electrode can distinguish presence of N. gonorrhoeae from Neisseria meningitidis and Escherichia coli culture and spiked samples from the urethral swabs of the patients.

Self-assembled monolayer for low density lipoprotein detection.

Heparin (HEP) has been covalently immobilized onto 4-aminothiophenol (ATP) self-assembled monolayer (SAM) deposited onto gold (Au)-coated glass plate for low density lipoprotein (LDL) detection. The HEP/ATP/Au and LDL/HEP/ATP/Au electrodes have been characterized using cyclic voltammetry (CV) and scanning electron microscopy (SEM). Surface plasmon resonance (SPR) measurements reveal that HEP/ATP/Au electrode is sensitive to detection of the LDL in the range 0.03 microM (10 mg/dl)-0.39 microM (130 mg/dl). The values of association and dissociation rate constants in the association phase calculated by kinetic analysis have been found to be k(a) = 9.67 x 10(1) M(-1) s(-1) and k(d) = 2.64 x 10(-4) s(-1).

Polyaniline Langmuir-Blodgett film based cholesterol biosensor.

Cholesterol oxidase (ChOx) has been covalently linked to Langmuir-Blodgett (LB) monolayers of polyaniline (PANI)-stearic acid (SA) prepared onto indium-tin-oxide (ITO) coated glass plates via glutaraldehyde (Glu) chemistry. These ChOx/Glu/PANI-SA LB film/ITO electrodes have been characterized by FT-IR, cyclic voltammetry, and scanning electron microscopy, respectively. The results of response measurements carried out on these bioelectrodes using linear sweep voltammetry (LSV) reveal linearity from 25 to 400 mg/dL of cholesterol concentration with sensitivity of 88.9 nA mg(-1) dL. The linear regression analysis of bioelectrode reveals standard deviation and correlation coefficient of 0.737 microA and 0.9988, respectively. The low value of the Michaelis-Menten constant of these bioelectrodes obtained as 1.21 mM for the immobilized enzyme indicates increased interaction between ChOx and cholesterol in the PANI-SA LB film.

Improved performance of polyaniline-uricase biosensor.

Uricase has been covalently immobilized using glutaraldehyde as cross-linker onto electrochemically synthesized polyaniline (PANI) films. These PANI-uricase electrodes have been characterized using spectroscopic, cyclic voltammetry and impedance measurements. The morphology and covalent linkage of uricase lead to high enzyme loading and better shelf life. The value of the Michaelis-Menton constant obtained as 5.1x10(-3) mM L(-1) for the immobilized uricase compared to 3.4x10(-1) mM L(-1) for the free uricase enzyme, suggests enhancement in affinity and/or activity of uricase attached to PANI. The influence of pH, temperature and concentration on electrode activity were studied. The enzyme electrodes were found to retain 95% of activity after 17-18 weeks when stored at 4 degrees C. These electrodes have a response time of about 60 s and have been used to measure uric acid concentration in serum. These PANI-uricase electrodes can be used for about 30 times for electrochemical measurements while retaining about 90% of its activity indicating improved performance.

Primitive neuroectodermal tumor of the uterus: a case report.

Peripheral primitive neuroectodermal tumor is a rare group of tumors belonging to the Ewing's family of tumors. The female genital tract is a rare site of origin and to date there are 14 reported cases in the literature. We hereby report the 15(th) case of uterine primitive neuroectodermal tumor in a 24-year-old multipara in the reproductive age group. A 24-year-old multipara presented with pain and mass abdomen. Physical examination revealed a pelvic mass enlarged to 20 weeks size gravid uterus, fixed, tender and hard, occupying the whole pelvis. Magnetic resonance imaging showed a large mass posterior to the uterus. She underwent panhysterectomy and debulking of the tumor. Histopathology confirmed the diagnosis. She developed recurrence of the tumor within a month and is now on chemotherapy.