Semiconductor biosensor

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Electrogenerated chemiluminescence (ECL) has proved to be useful for analytical applications including organic analysis, ECL-based immunosensors, DNA probe assays, and enzymatic biosensors. In the last few years, the electrochemistry and ECL of compound semiconductor nanocrystallites have attracted much attention due to their potential applications in analytical chemistry (ECL sensors). 

Curii ML, Agostiano A, Leo G, Mallardi A, Cosma P, Monica MD (2002) Development of a novel enzyme/semiconductor nanoparticles system for biosensor apphcation. Mater Sci Eng C 22 449-452... 

FIGURE 7.3 Simplified equivalent circuit of an original (unmodified) EIS structure (a) and EIS biosensor functionalized with charged macromolecules (b). Cj, Cx and CML are capacitances of the gate insulator, the space-charge region in the semiconductor, and the molecular layer, respectively / u is the resistance of... 

Field effect transistors are miniature, solid-state, potentiometric transducers (Figure 4.22) which can be readily mass produced. This makes them ideal for use as components in inexpensive, disposable biosensors and various types are being developed. The function of these semiconductor devices is based on the fact that when an ion is absorbed at the surface of the gate insulator (oxide) a corresponding charge will add at the semiconductor... 

The lure of new physical phenomena and new patterns of chemical reactivity has driven a tremendous surge in the study of nanoscale materials. This activity spans many areas of chemistry. In the specific field of electrochemistry, much of the activity has focused on several areas (a) electrocatalysis with nanoparticles (NPs) of metals supported on various substrates, for example, fuel-cell catalysts comprising Pt or Ag NPs supported on carbon [1,2], (b) the fundamental electrochemical behavior of NPs of noble metals, for example, quantized double-layer charging of thiol-capped Au NPs [3-5], (c) the electrochemical and photoelectrochemical behavior of semiconductor NPs [4, 6-8], and (d) biosensor applications of nanoparticles [9, 10]. These topics have received much attention, and relatively recent reviews of these areas are cited. Considerably less has been reported on the fundamental electrochemical behavior of electroactive NPs that do not fall within these categories. In particular, work is only beginning in the area of the electrochemistry of discrete, electroactive NPs. That is the topic of this review, which discusses the synthesis, interfacial immobilization and electrochemical behavior of electroactive NPs. The review is not intended to be an exhaustive treatment of the area, but rather to give a flavor of the types of systems that have been examined and the types of phenomena that can influence the electrochemical behavior of electroactive NPs. 

The history of electrochemical sensors began in the thirties of the twentieth century, when the pH-sensitive glass electrode was deployed, but no noteworthy development was carried out till the middle of that century. In 1956, Clark invented his oxygen-sensor based on a Ft electrode in 1959, the first piezoelectric mass-deposition sensor (a quartz crystal microbal-ance) was produced. In the sixties, the first biosensors (Clark and Lyons, 1962) and the first metal oxide semiconductor-based gas sensors (Taguchi, 1962) started to appear. 

The immune biosensor analysis was carried out in the SPR-4 M device produced by the Institute of Physics of Semiconductors of the Ukrainian National Academy of Sciences. SPR spectroscopy was carried out in the Kretschmann configuration using He-Ne laser ( i=632.8 nm), goniometer (G-5 M), glass prism (the angle at the basis 68°) and photodiode (FD 263). The optical contact between the prism and the metallic layer was achieved by the application of polyphenyl ether (refractive index n= 1.62). 

While the variety of NPs used in catalytic and sensor applications is extensive, this chapter will primarily focus on metallic and semiconductor NPs. The term functional nanoparticle will refer to a nanoparticle that interacts with a complementary molecule and facilitate an electrochemical process, integrating supramolecular and redox function. The chapter will first concentrate on the role of exo-active surfaces and core-based materials within sensor applications. Exo-active surfaces will be evaluated based upon their types of molecular receptors, ability to incorporate multiple chemical functionalities, selectivity toward distinct analytes, versatility as nanoscale receptors, and ability to modify electrodes via nanocomposite assemblies. Core-based materials will focus on electrochemical labeling and tagging methods for biosensor applications, as well as biological processes that generate an electrochemical response at their core. Finally, this chapter will shift its focus toward the catalytic nature of NPs, discussing electrochemical reactions and enhancement in electron transfer. 

Semiconductor NPs, such as CdS, are commonly used as labels for optical detection of bioanalytes due to their inherent fluorescent properties. Several reviews on semiconductor NPs as fluorescent labels for biosensors are currently available in the literature.53 However, since these fluorescent labels are beyond the scope of this chapter, only semiconductor NPs that involve electrochemical detection methods (stripping voltammetry or photoelectrochemical detection) will be discussed. 

B. Stein, M. George, H.E. Gaub, J.C. Behrends and W.J. Parak, Spatially resolved monitoring of cellular metabolic activity with a semiconductor-based biosensor, Biosens. Bioelectron., 18(1) (2003) 31-41. 

C. Menzel, T. Lerch, K. Schneider, R. Weidemann, C. Tollnick, G. Kretzmer, T. Scheper and K. Schuger, Application of biosensors with an electrolyte isolator semiconductor capacitor (EIS-CAP) transducer for process monitoring, Process Biochem., 33(2) (1998) 175-180. 

Semiconductor (transistor) biosensors are widely used. They possess a several process advantages over the others small size, good reproducibility and high sensitivity, multipurpose chip design, accessibility and low price. 

The use of nanoparticles has extended throughout the field of biosensors in the electrochemical detection of DNA and immunoreactions (Murphy 2006). A wide range of nanoparticles including nanotubes and nanowires, prepared from metals, semiconductor, carbon or polymeric species, have been investigated. The enhanced electrochemistry is due to the ability of the small nanoparticles to reduce the distance between the redox site of a protein and the electrode, since the rate of electron transfer is inversely dependent on the exponential distance between them (Balasubramanian and Burghard 2006). CNT-modified electrodes have been most frequently used for the development of biosensors (Gooding 2005). 

The first biosensor based on semiconductor technology was reported by Caras and Janata in 1980 (1). They developed a microbiosensor sensitive to penidllin based on a hydrogen ion-sensitive field effect transistor (FET) transducer in conjunction with a penicillinase-immobilized membrane. This type of biosensor offers discriminating advantages over the conventional counterpart with an electrode transducer (see Chapter 3) ... 

Semiconductor fabrication techniques have also been successfully applied to the construction of conventional transducers sensitive to hydrogen peroxide, oxygen, and carbon dioxide, A hydrogen peroxide-sensitive silicon chip was made by using metal deposition techniques (28,29). The combination of the hydrogen peroxide-sensitive transducer and enzyme-immobilized membranes gave a miniaturized and multifunctional biosensor. Similarly, an oxygen- and a carbon dioxide-sensitive device was made cmd applied to the construction of biosensors (25, 30, 31). 

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