Rapid Characterization of Monoclonal Antibodies using the Piezoelectric Immunosensor

Current Trends in the Biosensors for Biological Warfare Agents Assay

Biosensors are analytical devices combining a physical sensor with a part of biological origin providing sensitivity and selectivity toward analyte. Biological warfare agents are infectious microorganisms or toxins with the capability to harm or kill humans. They can be produced and spread by a military or misused by a terrorist group. For example, Bacillus anthracis, Francisella tularensis, Brucella sp., Yersinia pestis, staphylococcal enterotoxin B, botulinum toxin and orthopoxviruses are typical biological warfare agents. Biosensors for biological warfare agents serve as simple but reliable analytical tools for the both field and laboratory assay. There are examples of commercially available biosensors, but research and development of new types continue and their application in praxis can be expected in the future. This review summarizes the facts and role of biosensors in the biological warfare agents' assay, and shows current commercially available devices and trends in research of the news. Survey of actual literature is provided.

Evaluation of the Spectral Response of Functionalized Silk Inverse Opals as Colorimetric Immunosensors

Regenerated silk fibroin is a high molecular weight protein obtained by purifying the cocoons of the domesticated silkworm, Bombyx mori. This report exploits the aqueous processing and tunable β sheet secondary structure of regenerated silk to produce nanostructures (i.e., inverse opals) that can be used as colorimetric immunosensors. Such sensors would enable direct detection of antigens by changes in reflectance spectra induced by binding events within the nanostructure. Silk inverse opals were prepared by solution casting and annealing in a humidified atmosphere to render the silk insoluble. Next, antigen sensing capabilities were imparted to silk through a three step synthesis: coupling of avidin to silk surfaces, coupling of biotin to antibodies, and lastly antibody attachment to silk through avidin-biotin interactions. Varying the antibody enables detection of different antigens, as demonstrated using different protein antigens: antibodies, red fluorescent protein, and the beta subunit of cholera toxin. Antigen binding to sensors induces a red shift in the opal reflectance spectra, while sensors not exposed to antigen showed either no shift or a slight blue shift. This work constitutes a first step for the design of biopolymer-based optical systems that could directly detect antigens using commercially available reagents and environmentally friendly chemistries.

DETECTION OF CADMIUM-RESISTANT RHIZOBACTERIA USING PIEZOELECTRIC NANOBIOSENSOR

Traditionally, enzyme-linked immunosorbent assay (ELISA) is used for the interaction study of antibody–antigen ( Ab – Ag ) along with Western blot, immunofluorescence and flow cytometry. These are the processes which give the result at the end on the basis of amount of bound label. Piezoelectric quartz crystal microbalance (QCM) has more advantages like elimination of the use of the enzyme or radioactive-labelled material, simple concept, rapid turn-around time, cost effectiveness and easy automation over traditional techniques. Efforts are being made to enhance the efficacy of QCM biosensor by employing appropriate nanomaterials. In the present piece of work silver nanoparticles were prepared, characterized and applied on AT-cut gold-coated quartz crystal to get more surface area and hence more Ag – Ab complex. The gold electrode of quartz crystal modified with silver nanoparticles was exposed to antibody (anti-Rhizobacteria) and finally to the corresponding antigen (Rhizobacteria). The change in the resonant frequency of quartz crystal of QCM was measured after each modification. The sharp decrease in resonant frequency reflects the interaction of Rhizobacteria with its corresponding antibody (anti-Rhizobacteria). The signals obtained from such a nanobiosensor were compared with ELISA. A similar selectivity and higher sensitivity along with less time was observed with the developed QCM nanobiosensor.

Amperometric Biosensors for Real Time Assays of Organophosphates

An amperometric biosensor based on acetylcholinesterase (AChE) immobilized in gelatin was used to develop an assay for the organophosphate paraoxon. The more traditional manner employing preincubation was used for comparison between measurement procedures, although the aim of the study was to examine the performance of the biosensor for real time monitoring of organophosphates. The biosensor was immersed in a reaction chamber and paraoxon was injected inside. We were able to detect 200 pg of paraoxon within one minute or 2.5 ppb when the biosensor was preincubed in the sample solution for 15 minutes. The practical impact and expectations are discussed.

Diagnosis of Intoxication by the Organophosphate VX: Comparison Between an Electrochemical Sensor and Ellman´s Photometric Method

An electrochemical sensor is introduced as a tool applicable for diagnosis of intoxication by cholinesterase inhibitors caused by the well-known nerve agent VX. The traditional Ellman method was chosen for comparison with the sensor's analytical parameters. Both methods are based on estimation of blood cholinesterase inhibition as a marker of intoxication. While Ellman´s method provided a limit of detection of 5.2´10^-7 M for blood containing VX, the electrochemical sensor was able to detect 4.0´10^-7 M. Good correlation between both methods was observed (R = 0.92). The electrochemical sensor could be considered a convenient tool for a fast yet accurate method, easily available for field as well as laboratory use. Time and cost savings are key features of the sensor-based assay.

Piezoelectric Biosensor for a Simple Serological Diagnosis of Tularemia in Infected European Brown Hares (Lepus europaeus)

Piezoelectric biosensor was used for diagnosis of infection by Francisella tularensis subsp. holarctica in European brown hares. Two kinds of experiments were performed in this study. First, sera from experimentally infected European brown hares (Lepus europaeus) were assayed by piezoelectric biosensor and the seventh day post infection was found as the first one when statistically significant diagnosis of tularemia was possible; all other sera collected from hares later than on day 7 following the infection were found tularemia positive. Typing to classify the field strain of F. tularensis used for the experimental infection was confirmed by proteome study. Second, sera from 35 European brown hare specimens sampled at hunting grounds and tested as tularemia positive by slow agglutination allowed diagnosis of tularemia by the piezoelectric biosensor. All these sera of naturally infected hares were found as tularemia positive, too. Efficacy of the piezoelectric biosensor for the serological diagnosis of tularemia is discussed.