Mass sensitive biosensors represent promising tool that used in many areas such asbiomedical applications, food, environmental, military and in other fields instead of conventional methods. However, surface modifications are needed to design this rapid and reliable sensors. Plasma polymerization is a commonly used technology which offers easily-controllable, environmentally friendly, and inexpensive processing of various materials when compared to the wet chemical methods. This review includes working principle of mass sensitive biosensors, surface modification of piezoelectric crystals by plasma technology and applications of these crystals as a mass sensitive biosensor in biomedical applications.

As biomedical materials, titanium and titanium alloys (Ti-6Al-4V) are superior to many materials in terms of mechanical properties and biocompatibility. However, they are still not sufficient for prolonged clinical use because the biocompatibility of these materials must be improved. In this study, the prevention of the attachment of test microorganism on the Ti alloy surfaces by thiol (-SH) and hydroxyl (-OH) functional group containing monomer in plasma based electron beam generator was reported in order to prepare anti-fouling surfaces. The precursor, 11-mercaptoundecanoic acid is used as plasma source to create nano-film with 30-60 nm approximately. The surface chemistry and topology of uncoated and coated samples are characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM). Static contact angle measurements are performed to state the change of surface hydrophilicity. All coated samples are tested in-vitro environment with Staphylococcus epidermidis that is chosen as the test bacteria strain in view of its significance for the pathogenesis of medical-device-related infections. This test is repeated after certain period of times and samples are waited in dynamic fluid media in order to investigate the stability of nano-coating. Plasma polymerized 11-mercaptoundecanoic acid film (PP MUA) with 42 +/- 4 nm is found alternative, stabile and simple method to create bacterial anti-fouling surfaces. The static contact angle of the coated surface is 34 +/- 80 whereas the uncoated surface is 57 +/- 50. For the coated surface, the presence of C-OH and C==O groups in infrared spectra defining the PP MUA is achieved by the plasma polymerization. The attachment of the model microorganism on the biomaterial surface prepared by PP MUA is reduced 85.3% if compared to unmodified control surface.

The static and dynamic adsorption behaviors of a model protein “Bovine Serum Albumin” on plain (SS 316) and 2-hydroxethylmethacrylate (HEMA) or polyethyleneglycolmethacrylate (PEGMA) plasma polymerization (PlzP) modified stainless steel surfaces were studied. For equilibrium adsorption behavior, Freundlich model was attempted and model parameters for Freundlich (KF and n) were obtained. The values of the KF and n were 24.4, 0.88; 14.9, 0.83 and 19.7, 0.85 for, SS 316, PlzP(HEMA) and PlzP(PEGMA) surfaces, respectively. The results of “static” equilibrium adsorption studies showed that, a monolayer of the protein molecules formed next to the solid surface. The dynamic adsorption process reached to the plateau value around 160min for SS 316, 150min for PlzP(PEGMA) and 75min for PlzP(HEMA) surfaces. The total amount of BSA adsorbed on the SS 316, PlzP(HEMA) and PlzP(PEGMA) surfaces at the plateau were calculated as, 4.35, 2.77 and 0.38mg, respectively. A parameter to define the dynamic behavior of the adsorption so called “Initial adsorption rate” were introduced and calculated for of BSA adsorption on the SS 316, PlzP(HEMA) and PlzP(PEGMA) surfaces as, 33×10−7, 3×10−7 and 10×10−7g/mincm2, respectively. These dynamic results are in a very good agreement with the results obtained in static adsorption tests.

This paper describes a method for the modification of quartz crystal surfaces to be used as a transducer in biosensors that allow recognition and quantification of certain biomolecules (antibodies, enzymes, proteins, etc). Quartz crystal sensors were modified by a plasma based electron beam generator in order to detect the level of the toxin histamine within biological liquids (blood, serum) and food (wine, cheese, fish etc.). Cysteamine and ethylenediamine were used as precursors in the plasma. After each modification step, the layers on the quartz crystal were characterized by frequency measurements. Modified surfaces were also characterized by contact angle, X-ray photoelectron spectroscopy and atomic force microscopy to determine the physical and chemical characteristics of the surfaces after each modification. Finally, the performance of the sensors were tested by the response to histamine via frequency shifts. The frequency shifts of the sensors prepared by plasma polymerization of ethylenediamine and cysteamine were approximately 3230 Hz and 5630 Hz, respectively, whereas the frequency change of the unmodified crystal surface was around 575 Hz. (C) 2007 Elsevier B.V. All rights reserved.

The aim of this study is to develop an immunoaffinity sensor based on piezoelectric crystals for human serum albumin (HSA) detection in aqueous media. Quartz crystals were treated with ethylene diamine (EDA) plasma in a glow-discharge apparatus in order to substitute amino groups on their surfaces. Then anti-HSA antibodies were immobilized via these amino groups by using glutaraldehyde (GA) as cross-linker. Immobilization of the antibody on the quartz crystal was examined for different pH, antibody concentration and treatment time. The optimum conditions for anti-HSA immobilization were evaluated by the measurements of the activity of the surface against HSA. The optimum values of pH, antibody concentration and treatment time were found 6.2, 0.15 mg/ml and 2 h, respectively. For detection of HSA into the solution, two methods were used. In the first (dip and dry) method, the frequency shifts were measured in air after the 1 h interaction of the anti-HSA immobilized crystals with HSA solution. In the other (direct) method, the frequency shifts were followed continuously for 60 min. while the probe was immersed in the HSA solution. An increase for the frequency shifts was observed with increasing of HSA concentration of 16–128 μg/ml. Both the immobilization and antibody-interaction conditions were found important on the extend of these specific interaction. The relations between the HSA concentrations and frequency shifts were exponential in both methods.

Cellulose acetate membranes (CA) were modified by means of plasma polymerization of ethylene diamine (EDA) and n-butylamine (n-BA). The motivation for this work was the application of a modified membrane for the single-layer enzyme electrode. A tubular reactor with the external radiofrequency (13.56 MHz) excitation was used. Surface modification was performed at 5, 10, and 15 W power (at 27 Pa working pressure) for 5, 10, 15 min. Modified surfaces were characterized in detail by FTIR-ATR, XPS (ESCA), contact angle, and enzyme immobilization activity. The best treatment results were obtained for EDA with 5 W and 30 min and 15 W and 10 min. These results are discussed using surface analysis data. (C) 2001 John Wiley & Sons, Inc.

The aim of this study was to develop a single-layer glucose enzyme electrode with extended linearity to be used in the food industry in order to determine the glucose content. An amperometric-based probe-type glucose enzyme electrode with Pt working electrode and Ag/AgCl reference electrode polarised at +650 mV was used. In this study, permselective behaviour of different polymeric membranes, which were prepared in our laboratory (cellulose acetate, polyurethane, polyetersulphone) and commercially available tract-etched polycarbonate, were investigated at different pH values (pH 4, 6, 7.4, 10) to estimate the magnitude of interferences caused by a group of different electroactive compounds. The selectivity tests showed that cellulose acetate membranes were the most convenient structure to establish a single-membrane recognition layer. The single surface of the cellulose acetate membranes was then modified with a plasma polymerisation technique at different glow-discharge parameters with amylamine monomer in order to show the effect of plasma polymerisation. The plasma-treated surface of the membranes was activated with glutaraldehyde then glucose oxidase (GOD) immobilised onto this site. The linearity and response time of these electrodes were investigated at pH 4 and 6. According to the results of linearity and response time tests, cellulose acetate membranes treated with amylamine at 5 W/20 min showed the best result. The linearity and response time of this electrode were found to be 320 mM glucose and 500 s, repectively at pH 4. Finally, the GOD electrode which was prepared with the most convenient membrane was used to determine the glucose content of some food stuff. Similar results were observed with the conventional measurement method.

The formation of the enzyme layer of the sandwich type electrodes has been altered and evaluated in terms of kinetic performance. The detection of H2O2 serves to measure the extent of the reaction. The kinetics of the recognition layer are discussed in terms of the response time of the electrode. The enzyme loading between two membranes has altered mass transfer limitations resulting in significant changes in the response of the electrode. The effectiveness factor is used to describe the mass transfer limitations in the system. The response time of the electrode has been increased while the effectiveness factor has been decreased. Steady-state response of the electrodes has been achieved in 43.68 and 98 s for the electrodes including 23.1%, 13.0% and 7.0% (w/w) GOD in a BSA + GOD mixture, respectively. The effectiveness factors for these electrodes have been established at the values of 0.59, 0.38 and 0.16, respectively.

A plasma polymerisation technique was used to prepare high linearityamperometric enzyme electrodes. Two different types of recognition layer for glucose based on oxidases were studied. The first type of recognition layer was prepared in sandwich form with polyethersulphone (PES) and polycarbonate (PC) membranes which were used as inner and outer membranes, respectively. Glucose oxidase was entrapped between these two membranes. The outer surface of PC membranes were further modified by deposition of hexamethyldisiloxane (HMDS) in a glow-discharge reactor-to improve linearity. A new type of recognition layer in the form of a single membrane was prepared from cellulose acetate (CA). One surface of the cellulose acetate membrane was modified by deposition of amylamine (AmA) by plasma polymerisation to substitute amino groups on the membrane surface for glucose oxidase immobilisation, Both types of recognition layers were placed separately on a probe type oxygen electrode system with Pt working electrode and Ag/AgCl reference electrode which was polarised at 650 mV. Linearity of these enzyme electrodes were investigated. The linearity of the sandwich type electrode was extended to 600 mM glucose by surface modification of the outer membrane by glow-discharge deposition of hexamethyldisiloxane. The linearity of the single layer enzyme electrode was found to be 1000 mM glucose.

Contralateral testicular perfusion during unilateral testicular torsion was evaluated using simultaneous blood flow and O2 content determinations. Two groups, each consisting of 7 rats, were studied. Sham operation or 720 degrees clockwise twisting was performed on the left testes, and blood flow, O2 content and temperatures were monitored in the right testes for 180 min. An ultrasonic perivascular Doppler flowmeter system, an electronic thermometer and an O2 electrode were used for the monitoring. The contralateral testicular blood flow and relative O2 contents were stable in the control group. However, the initial and 180 min blood flow values decreased from 0.21 +/- 0.04 to 0.11 +/- 0.02 ml/min (p < 0.001), and the O2 contents from 0.857 +/- 0.123 to 0.319 +/- 0.037 (1.0 corresponds to 19.6 mm Hg pO2, p < 0.05) in the experimental group. Unilateral testicular torsion decreases the blood flow and O2 content of the contralateral testis. The contralateral testicular injury encountered following unilateral testicular torsion might result from hypoxia following the decrease in blood flow.

A Clark type, amperometric, multienzyme electrode, employing glucose oxidase and mutarotase, was used to determine the enzymatic activity of a model enzyme, invertase, in soluble and immobilized forms. A calibration curve with linear range up to 70 IU of invertase activity corresponding to the 6.0 nA/s of electrode response was sketched. It is shown that, multienzyme electrodes can be utilized as a very rapid, reliable and sensitive tool for the determination of enzymatic activity either in a free or immobilized form.

The influence of cross-linker density (2%, 5% and 10% of glutaraldehyde) on the permeability, P, of the enzyme layer (267.7, 203.5 and 146.0 μm/s respectively for 125I-cortisol-histamine conjugate, CHC (MW: 651) as tracer) in Clark enzyme electrode is reported. A diffusion chamber technique based on unsteady-state analysis for the estimation of permeabilities of radiolabelled molecules through enzyme layer is performed.

Sandwich type amperometric enzyme electrodes for glucose based on oxidases were studied. Polyethersulphone (PES) and polycarbonate (PC) membranes were used as inner and outer membranes, respectively. Glucose oxidase was entrapped between these two membranes. The selectivity of the inner membrane against a group of electroactive compounds in blood were tested. The PES membrane fulfilled all the requirements of a permselective membrane. The outer surface of PC membranes were further modified by deposition of hexamethyldisiloxane (HMDS) in a glow-discharge reactor or by coating with polyvinylalcohol (PVAL) to increase the linear range of the electrode while keeping or improving the blood-compatible properties of membrane. Linearity of these enzyme electrodes were investigated in different media (i.e., buffer solutions, blood plasma and blood). Blood-compatibilities of the PC membrane and its modified forms were obtained in in-vitro experiments. HMDS treatment significantly increased the linearity of enzyme electrode but did not affect their blood-compatibilities or significantly change the selectively. Also, the PVAL coating, considerably, extended the linear range of the electrode, slightly improved blood-compatibility but did not change the selectivity.