Prospects of conducting polymers in biosensors

DNA entrapped polypyrrole–polyvinyl sulfonate film for application to electrochemical biosensor

Double-stranded calf thymus (dsCT)-DNA was electrochemically entrapped into polypyrrole-polyvinyl sulfonate (PPy-PVS) films deposited onto indium tin oxide (ITO) coated glass plates. These dsCT-DNA entrapped PPy-PVS/ITO films were characterized using cyclic voltammetry, UV-visible, Fourier transform infrared (FT-IR), scanning tunneling microscopy (STM), and electrochemical impedance measurements. Attempts made to use these dsCT-DNA entrapped PPy-PVS/ITO films for detection of 2-aminoanthracene (0.001-6.0 ppm) and 3-chlorophenol (0.01-55.0 ppm) revealed a response time of 30s and a shelf life of approximately 25 weeks when stored under desiccated conditions at 25 degrees C. The addition of salts such as Ca(2+) (250 ppm), Mg(2+) (200 ppm), Cl(-) (1560 ppm), and Na(+) (150 ppm) ions contained in water does not affect the observed amperometric response of the disposable dsCT-DNA entrapped PPy-PVS film-based electrochemical biosensor.

Cholesterol biosensor based on amino-undecanethiol self-assembled monolayer using surface plasmon resonance technique

Cholesterol oxidase has been covalently immobilized onto 11-amino-1-undecanethiol hydrochloride (AUT) self-assembled monolayer (SAM) fabricated on gold (Au) substrates using glutaraldehyde as a cross-linker. These ChOx/AUT/Au bioelectrodes characterized using contact angle (CA) measurements; electrochemical technique and atomic force microscopy (AFM) have been utilized for the estimation of cholesterol in solution using the surface plasmon resonance (SPR) technique. These biosensing electrodes exhibiting linearity from 50 to 500 mg/dL of cholesterol in solution and sensitivity of 1.23 m0/(mg dL), can be used more than 20 times and have a shelf life of about 10 weeks when stored at 4 degrees C.

Advantages and limitations of on-line solid phase extraction coupled to liquid chromatography–mass spectrometry technologies versus biosensors for monitoring of emerging contaminants in water

On-line solid phase extraction (SPE) coupled to liquid chromatography-mass spectrometry (LC-MS) and biosensors are advanced technologies that have found increasing application in the analysis of environmental contaminants although their application to the determination of emerging contaminants (previously unknown or unrecognized pollutants) has been still limited. This review covers the most recent advances occurred in the areas of on-line SPE-LC-MS and biosensors, discusses and compares the main strengths and limitations of the two approaches, and examines their most relevant applications to the analysis of emerging contaminants in environmental waters. So far, the on-line configuration most frequently used has been SPE coupled to liquid chromatography-(tandem) mass spectrometry. Sorbents used for on-line SPE have included both traditional (alkyl-bonded silicas and polymers) and novel (restricted access materials (RAMs), molecularly imprinted synthetic polymers (MIPs), and immobilized receptors or antibodies (immunosorbents) materials. The biosensor technologies most frequently applied have been based on the use of antibodies and, to a lesser extent, enzymes, bacteria, receptors and DNA as recognition elements, and the use of optical and electrochemical transducing elements. Emerging contaminants investigated by means of these two techniques have included pharmaceuticals, endocrine disrupting compounds such as estrogens, alkylphenols and bisphenol A, pesticides transformation products, disinfection by-products, and bacterial toxins and mycotoxins, among others. Both techniques offer advantageous, and frequently comparable, features such as high sensitivity and selectivity, minimum sample manipulation, and automation. Biosensors are, in addition, relatively cheap and fast, which make them ideally suited for routine testing and screening of samples; however, in most cases, they can not compete yet with on-line SPE procedures in terms of accuracy, reproducibility, reliability (confirmation) of results, and capacity for multi-analyte determination.

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.

Cholesterol biosensor based on N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane self-assembled monolayer

Cholesterol oxidase (ChOx) has been covalently immobilized onto two-dimensional self-assembled monolayer (SAM) of N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTS) deposited on the indium-tin oxide (ITO) coated glass plates using N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) chemistry. These ChO x/AEAPTS/ITO bioelectrodes are characterized using contact angle (CA) measurements, UV-visible spectroscopy, atomic force microscopy (AFM), electrochemical impedance technique, and Fourier transform infrared (FT-IR) technique. The covalently immobilized ChOx-modified AEAPTS bioelectrodes are used for the estimation of cholesterol in solution using UV-visible technique. These cholesterol sensing bioelectrodes show linearity as 50 to 500 mg/dl for cholesterol solution, detection limit as 25mg/dl, sensitivity as 4.499 x 10(-5) Abs (mg/dl)(-1), K(m) value as 58.137 mg/dl (1.5mM), apparent enzyme activity as 1.81 x 10(-3) U cm(-2), shelf life of approximately 10 weeks, and electrode reusability as 10 times.

Polypyrrole nanotube array sensor for enhanced adsorption of glucose oxidase in glucose biosensors

A novel amperometric biosensor based on polypyrrole (PPy) nanotube array deposited on a Pt plated nano-porous alumina substrate and its performances are described. Glucose oxidase (GOx) enzyme was selected as the model enzyme in this study. Commercially available nano-porous alumina discs were used to fabricate electrodes in order to study the feasibility of enzyme entrapment by physical adsorption. A PPy/PF6- film comprising of nanotube array was synthesized using a solution containing 0.05 M Pyrrole and 0.1 M NaPF6 at a current density of 0.3 mA/cm2 for 90 s. The immobilization was done by physical adsorption of 5 microL of GOx (from a stock solution of 2 mg/mL of 210 U/mg) on each electrode. A sensitivity of 7.4 mA cm(-2) M(-1) was observed with PPy nanotube array where the maximum tube diameter was 100 nm. A linear range of 500 microM-13 mM and a response time of about 3 s were observed with a nanotube array where the maximum tube diameter was 200 nm. The synthesized nanotube arrays were characterized by galvanostatic electrochemical technique. Calculated value of apparent Michaelis-Menten constant (Km) was 7.01 mM. The use of nano-porous template electrodes leads to an efficient enzyme loading and provides an increased surface area for sensing the reaction. These factors contribute to increase the characteristic performances of the novel biosensor.

Application of thiolated gold nanoparticles for the enhancement of glucose oxidase activity

Glucose oxidase (GOx) has been covalently immobilized onto chemically synthesized thiolated gold nanoparticles (5-8 nm) via N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The lower value of the Michaelis-Menton constant obtained for the immobilized (3.74 mM) GOx compared with that for the free (5.85 mM) GOx suggests significant enhancement in the activity of GOx attached to thiolated gold nanoparticles. The covalently immobilized GOx thiolated nanoparticles exhibit a response time of 30 s, a shelf life of more than 6 months, and improved tolerance to both pH and temperature.

Dithiobissuccinimidyl propionate self assembled monolayer based cholesterol biosensor

A dithiobissuccinimidyl propionate (DTSP) self-assembled monolayer (SAM) prepared onto a gold (Au) surface has been utilized for covalent immobilization of cholesterol oxidase (ChOx) and cholesterol esterase (ChEt). These ChOx-ChEt/DTSP/Au bio-electrodes have been characterized using electrochemical impedance and cyclic voltammetric (CV) techniques, respectively. Differential pulse voltammetry (DPV) has been used for enzymatic assay of immobilized ChOx and ChEt onto the DTSP modified gold surface as a function of cholesterol oleate concentration. The response measurement conducted on ChOx-ChEt/DTSP/Au bio-electrode reveal the value of Michaelis-Menten constant (Km) as 0.95 mM suggesting enhanced affinity of enzymes (ChOx and ChEt). The ChOx-ChEt/DTSP/Au bio-electrodes show linearity in range of 50 to 400 mg dl(-1) of cholesterol oleate and the shelf-life of more than 50 days when stored at 4 degrees C. This biosensing electrode shows correlation coefficient of 0.9973 and standard deviation of regression as 0.859 microA.