RESUMO
Despite the multitude of different parameters currently measured in the clinical laboratory, only a minor part of these are measured by means of biosensor-based methods. Within the group of biochemical sensors, enzyme or metabolic sensors as integrated devices in clinical analyzers are dominating. Economically most important are sensors for measuring blood glucose. The implementation of lactate and urea sensors in commercial analytical systems is just beginning and a few more analytes are being intensively investigated in research laboratories (1). Thus, it seems that metabolic biosensors slowly leave the academic playground.
RESUMO
This chapter demonstrates a preliminary experimental approach to detect antiviral antibodies by means of a quartz crystal immunosensor. As an example of the large numbers of immunoassays currently applied in the clinical laboratory, the screening for human immunodeficiency virus (HIV) specific antibodies was presented as a model application. The quartz crystal microbalance belongs to the group of acoustic immunosensors and its principle of operation is based on the propagation of acoustic shear waves in the substrate of the sensor. Phase and velocity of the acoustic wave are influenced by the specific adsorption of antibody molecules onto the antigen-coated sensor surface. This primary measuring allows the continuous monitoring of molecular interactions in liquids.
RESUMO
The detection of anti-human immunodeficiency virus (HIV) antibodies by means of synthetic HIV peptide immobilized on a piezoelectric quartz sensor is demonstrated. The measurement set-up consists of an oscillator circuit, a suitably modified AT-cut thickness-shear-mode quartz crystal with gold electrodes, which is housed in a special reaction vessel, and a computer-controlled frequency counter for the registration of the measured frequency values. The quartz crystal is adapted for a steady operation in liquids at a frequency of 20 MHz. In phosphate-buffered saline solution the oscillator reaches a stability of about 0.5 Hz within a few seconds, of about 2 Hz within 10 min and about 30 Hz within 1 h. The frequency shift due to the adsorption of various proteins to the uncoated sensor surface has been investigated. It can be shown that a stable adsorptive binding of proteins to an oscillating gold surface is feasible and can be used for the immobilization of a receptor layer (e.g. HIV peptide). Specific binding of the anti-HIV monoclonal antibody to the HIV peptide immobilized on the quartz sensor is demonstrated. Control experiments show, however, additional unspecific binding. According to the experiments, the Sauerbrey formula gives a sufficiently accurate value for the decrease of the resonant frequency due to adsorption or binding of macromolecular proteins on the quartz crystal surface.
