Hitoshi Muguruma

Plasma-polymerized films for biosensors II

Biosensors are devices that use a biological reaction for detecting target analytes by generating a quantifiable electronic signal. They are powerful tools used in medical diagnostics, food-quality control and environmental monitoring. A typical biosensor is an integrated product, incorporating biological elements and transducers. It has been consistently shown that plasma-polymerized thin films (PPFs), created in a glow-discharge or plasma-in-vapor phase, have potential for use as the interface between the two components of biosensors. This review mainly covers the developments in PPFs used for biosensor design since that previous review [H. Muguruma, I. Karube, Trends Anal. Chem. 18 (1999) 62]. To date, transducers have been amenable to miniaturization, and the concept of biosensors has concomitantly expanded to encompass microchips, arrayed sensors and nanotechnology. The role of dry-process-based PPFs in biosensor design has become increasingly more important.

Amperometric biosensor based on multilayer containing carbon nanotube, plasma-polymerized film, electron transfer mediator phenothiazine, and glucose dehydrogenase.

We report on a novel fabrication approach of amperometric biosensor based on multilayer films containing carbon nanotubes (CNT), a nano-thin plasma-polymerized film (PPF), electron transfer mediator phenothiazine (PT), and enzyme glucose dehydrogenase (GDH). The configuration of the electrochemical electrode is sequentially composed of sputtered gold, acetonitrile PPF, PT, GDH, and acetonitrile PPF (denoted as PPF/GDH/PT/CNT/PPF/Au). First PPF deposited on Au acts as a permselective membrane and as a scaffold for CNT layer formation. Second PPF directly deposited on GDH acts as a matrix for enzyme immobilization. To facilitate the electrochemical communication between the CNT layer and GDH, CNT was treated with nitrogen plasma. The electron transfer mediator PT plays a role as the mediator in which the electron caused by enzymatic reaction transports to the electrode. The synergy between the mediator and CNT provides benefits in terms of lowering the operational potential and enhancing the sensitivity (current). The optimized glucose biosensor revealed a sensitivity of 5.1 ± 0.9 μA mM(-1) cm(-2) at + 0.2V vs. Ag/AgCl, linear dynamic range of 4.9-19 mM, and a response time of 5 ± 1 s. Unlike conventional wet-chemical processes that are incompatible with mass production techniques, this dry-chemistry procedure has great potential for enabling high-throughput production of bioelectronic devices. Furthermore, those devices can be applied and expands for the cell biological functional field as a useful, helpful, or indispensable tool.

Recognition of sialic acid using molecularly imprinted polymer

Abstract The molecular imprinting technique was applied for the preparation of a polymer selective for sialic acid. To evaluate its binding ability the molecularly imprinted polymer obtained was used as a stationary phase in liquid chromatography. The polymer showed pH-dependent characteristics for binding: an optimum specificity to sialic acid at pH 8.1 and a higher affinity with group selectivity for cis-diol containing sugars at higher pH.

Mass transport behavior of electrochemical species through plasma-polymerized thin film on platinum electrode

Abstract We propose a novel method for generating thin film coating for use on a platinum (Pt) electrode. This is accomplished by a plasma-polymerized film (PPF), which is deposited directly onto the substrate under dry condition. The resulting films are extremely thin (

Integration of microfabricated needle-type glucose sensor devices with a novel thin-film Ag/AgCl electrode and plasma-polymerized thin film: mass production techniques.

We developed an integrated array of needle-type biosensors employing a novel process of fabrication, comprising conventional semiconductor fabrication and micromachining technology. Amperometric sensing electrodes with plasma-polymerized films and a thin-film Ag/AgCl reference electrode were directly integrated on a glass substrate with thin-film process, e.g., sputtering. An enzyme was immobilized on the electrode via the plasma-polymerized film, which was deposited directly on the substrate using a dry process. The novel thin-film Ag/AgCl reference electrode showed stable potentials in concentrated chloride solutions for a long period. The plasma-polymerized film is considered to play an important role as an interfacial design between the sensing electrode and the immobilized enzyme considering that the film is extremely thin, adheres well to the substrate (electrode) and has a highly cross-linked network structure and functional groups, such as amino groups. The results showed increments of the sensor signal, probably because the plasma-polymerized film allowed a large amount of enzyme to be immobilized. The greatest advantage is that the process can permit the mass production of high-quality biosensors at a low cost.

Light Dose and Time Dependency of Photodynamic Cell Membrane Damage

We have investigated the light dose and time dependency of photodynamic cell membrane damage using electrophysiological methods. This study controls the level of cell membrane damage by precisely administration of the light dose. The photosensitizer used was 5′,5″‐bis(aminomethyl)‐2,2′:5′,2″‐terthiophene dihydrochloride (BAT). A confocal laser scanning microscope was used to provide rapid light activation (<1 s) and the subsequent membrane damage was monitored using standard patch clamp techniques. In the presence of 49 μM BAT, light levels less than 0.94 J/cm2 led to a reversible depolarization (20 mV) and reduction of resistance (10%) within 3 s of illumination. Higher intensities of illumination (1.57 J/cm2) caused a complete and irreversible loss of membrane potential and cell membrane resistance within 8 s of illumination. The threshold dose of light required to induce cell death by illumination in the presence of BAT was increased in the presence of the antioxidant Trolox‐C.

Enzyme biosensor based on plasma-polymerized film-covered carbon nanotube layer grown directly on a flat substrate

We report a novel approach to fabrication of an amperometric biosensor with an enzyme, a plasma-polymerized film (PPF), and carbon nanotubes (CNTs). The CNTs were grown directly on an island-patterned Co/Ti/Cr layer on a glass substrate by microwave plasma enhanced chemical vapor deposition. The as-grown CNTs were subsequently treated by nitrogen plasma, which changed the surface from hydrophobic to hydrophilic in order to obtain an electrochemical contact between the CNTs and enzymes. A glucose oxidase (GOx) enzyme was then adsorbed onto the CNT surface and directly treated with acetonitrile plasma to overcoat the GOx layer with a PPF. This fabrication process provides a robust design of CNT-based enzyme biosensor, because of all processes are dry except the procedure for enzyme immobilization. The main novelty of the present methodology lies in the PPF and/or plasma processes. The optimized glucose biosensor revealed a high sensitivity of 38 μA mM(-1) cm(-2), a broad linear dynamic range of 0.25-19 mM (correlation coefficient of 0.994), selectivity toward an interferent (ascorbic acid), and a fast response time of 7 s. The background current was much smaller in magnitude than the current due to 10 mM glucose response. The low limit of detection was 34 μM (S/N = 3). All results strongly suggest that a plasma-polymerized process can provide a new platform for CNT-based biosensor design.

Detection of the red tide-causing plankton Alexandrium affine by a piezoelectric immunosensor using a novel method of immobilizing antibodies

In this paper, the determination of Alexandrium affine in sea water was performed using piezoelectric immunosensors. In addition, we report a novel method of immobilizing antibodies on the quartz crystal immunosensors using plasma-polymerized ethylenediamine film. The films formed on the quartz crystals are extremely thin, homogeneous and incorporate amino groups. Sensors produced using this method show higher sensitivity than sensors made using conventional immobilization methods for example polyethylenimine or γ-aminopropyltrimethoxysilane.

Electronically type-sorted carbon nanotube-based electrochemical biosensors with glucose oxidase and dehydrogenase.

An electrochemical enzyme biosensor with electronically type-sorted (metallic and semiconducting) single-walled carbon nanotubes (SWNTs) for use in aqueous media is presented. This research investigates how the electronic types of SWNTs influence the amperometric response of enzyme biosensors. To conduct a clear evaluation, a simple layer-by-layer process based on a plasma-polymerized nano thin film (PPF) was adopted because a PPF is an inactive matrix that can form a well-defined nanostructure composed of SWNTs and enzyme. For a biosensor with the glucose oxidase (GOx) enzyme in the presence of oxygen, the response of a metallic SWNT-GOx electrode was 2 times larger than that of a semiconducting SWNT-GOx electrode. In contrast, in the absence of oxygen, the response of the semiconducting SWNT-GOx electrode was retained, whereas that of the metallic SWNT-GOx electrode was significantly reduced. This indicates that direct electron transfer occurred with the semiconducting SWNT-GOx electrode, whereas the metallic SWNT-GOx electrode was dominated by a hydrogen peroxide pathway caused by an enzymatic reaction. For a biosensor with the glucose dehydrogenase (GDH; oxygen-independent catalysis) enzyme, the response of the semiconducting SWNT-GDH electrode was 4 times larger than that of the metallic SWNT-GDH electrode. Electrochemical impedance spectroscopy was used to show that the semiconducting SWNT network has less resistance for electron transfer than the metallic SWNT network. Therefore, it was concluded that semiconducting SWNTs are more suitable than metallic SWNTs for electrochemical enzyme biosensors in terms of direct electron transfer as a detection mechanism. This study makes a valuable contribution toward the development of electrochemical biosensors that employ sorted SWNTs and various enzymes.

Molecular imprinting of methyl pyrazines

Methyl pyrazines, particularly 2,5-dimethylpyrazine (DMP) and 2,3,5-trimethylpyrazine (3MP) are among the major flavor compounds associated with various seed and grain food processing operations, including roasting and drying. Synthetic polymers selective for DMP and 3MP were prepared by a molecular imprinting technique, and the binding characteristics of the imprinted polymers were examined by chromatographic methods. Despite the low molecular weight and lack of strongly interacting pendant functional groups in the pyrazine targets, the polymers showed selectivity for their respective templates over other pyrazines. Such polymers are envisioned to be of potential use in the analysis of flavor compounds in the food industry and in the selective isolation or enrichment of flavor profiles.