Recent Achievements in Electrochemical and Surface Plasmon Resonance Aptasensors for Mycotoxins Detection

Mycotoxins are secondary metabolites of fungi that contaminate agriculture products. Their release in the environment can cause severe damage to human health. Aptasensors are compact analytical devices that are intended for the fast and reliable detection of various species able to specifically interact with aptamers attached to the transducer surface. In this review, assembly of electrochemical and surface plasmon resonance (SPR) aptasensors are considered with emphasis on the mechanism of signal generation. Moreover, the properties of mycotoxins and the aptamers selected for their recognition are briefly considered. The analytical performance of biosensors developed within last three years makes it possible to determine mycotoxin residues in water and agriculture/food products on the levels below their maximal admissible concentrations. Requirements for the development of sample treatment and future trends in aptasensors are also discussed.

Biofunctionalized Two-dimensional MoS2 Receptors for Rapid Response Modular Electronic SARS-CoV-2 and Influenza A Antigen Sensors

Multiplex electronic antigen sensors for detection of SARS-Cov-2 spike glycoproteins or hemagglutinin from Influenza A in liquid samples with characteristics resembling extracted saliva were fabricated using scalable processes with potential for economical mass-production. The sensors utilize the sensitivity and surface chemistry of a two-dimensional MoS2 transducer for attachment of antibody fragments in a conformation favorable for antigen binding. Ultra-thin layers (3 nm) of amorphous MoS2 were directly sputtered over the entire sensor chip at room temperature and laser annealed to create an array of semiconducting 2H-MoS2 active sensor regions between metal contacts. The semiconducting region was functionalized with monoclonal antibody Fab (fragment antigen binding) fragments derived from whole antibodies complementary to either SARS-CoV-2 S1 spike protein or Influenza A hemagglutinin using a papain digestion to cleave the antibodies at the disulfide hinges. The high affinity for the MoS2 transducer surface with some density of sulfur vacancies for the antibody fragment base promoted chemisorption with antigen binding regions oriented for interaction with the sample. The angiostatin converting enzyme 2 (ACE2) receptor protein for the SARS-CoV-2 spike glycoprotein, was tethered to a hexa-histidine (his6) tag at its c-terminus both for purification purposes, as well as a motif for binding to MoS2. This modified protein was also investigated as a bio-recognition element. Electrical resistance measurements of sensors functionalized with antibody fragments and exposed to antigen concentrations ranging from 2-20,000 picograms per milliliter revealed selective responses in the presence of complementary antigens with sensitivity to SARS-CoV-2 or influenza A on the order of pg/mL and comparable to gold-standard diagnostics such as Polymerase Chain Reaction (PCR) analysis. Lack of antigen sensitivity for the larger ACE2 BRE further demonstrates the utility of the engineered antibody fragment/transducer interface in bringing the target antigen closer to the transducer surface for sensitivity required for early detection viral diagnostics.

Antibody-Electroactive Probe Conjugates Based Electrochemical Immunosensors

Suitable immobilization of a biorecognition element, such as an antigen or antibody, on a transducer surface is essential for development of sensitive and analytically reliable immunosensors. In this review, we report on (1) methods of antibody prefunctionalization using electroactive probes, (2) methods for immobilization of such conjugates on the surfaces of electrodes in electrochemical immunosensor construction and (3) the use of antibody-electroactive probe conjugates as bioreceptors and sensor signal generators. We focus on different strategies of antibody functionalization using the redox active probes ferrocene (Fc), anthraquinone (AQ), thionine (Thi), cobalt(III) bipyridine (Co(bpy)33+), Ru(bpy)32+ and horseradish peroxidase (HRP). In addition, new possibilities for antibody functionalization based on bioconjugation techniques are presented. We discuss strategies of specific, quantitative antigen detection based on (i) a sandwich format and (ii) a direct signal generation scheme. Further, the integration of different nanomaterials in the construction of these immunosensors is presented. Lastly, we report the use of a redox probe strategy in multiplexed analyte detection.

Підготовка компонентів селективної поверхні трансдюсера імунного біосенсора для індикації Pseudomonas aeruginosa

The article presents the results of research to obtain specific components of the preparation selective biosensor surface for further development the immune biosensor test-system for the express – indication of bacteria Pseudomonas aeruginosa and their detection in biological material and in the environment. Specific antiserum and immunoglobulins to P. aeruginosa were obtained by autors. The resulting surface modification components for activity and specificity of the specific compounents were tested using analytical device imunosensor «Plasmon-6», based on surface plasmon resonance. Biosensors are defined as any measuring device that contains a biological element. It combines the exquisite selectivity of biology with the processing power of modern microelectronics and optoelectronics to offer powerful new analytical tools with major applications in the field of medicine, environmental studies, food and processing industries. These analytical devices are based on the union between biological and physio-chemical components. Biological components include macro-molecules such as antibodies, enzymes, tissue slices which are used to recognize and interact with a specific analyte. Physiochemical components are usually referred to as transducers which converts the interactions into signals; it is later amplified with respect to its concentration of analyte. The transducer may use potentiometric, amperometric, optical, magnetic, colorimetric devices. A target analyte in the external membrane must be able to enter the biosensor. The external membrane of the biosensor must be permeable to the analyte where the biosensor is sensitive to it. The biological element inside the biosensor then interacts with chemical species through a biochemical reaction which in turn produces another chemical product and characterized by change in mechanical, electrical properties. The output signal may be a conventional electrochemical signal depending on the type of transducer it uses. Assessment of P. aeruginosa was carried out using an analytical device - immunosensor, with immobilized specific antibodies on the transducer surface. The antibodies have interact with cell antigens, and the resulting shift value resonance angle recorded. Changing the angle depends on the amount of the immune complexes formed on the transducer surface. From the obtained results on the selective surface of transducer of the imunosensor, we can see, that the diagnostic system works with IgG concentration of 1 mg/ml, working titer of 1:7 in polyclonal antibodies against P. aeruginosa. The resulting antiserum specific immunoglobulins can be used in preparing the selective surface of immune biosensor.

CMUTs in Permanent Contact Operation for High Output Pressure

We present the operation of capacitive micromachined ultrasonic transducers (CMUTs) in permanent contact mode as an efficient transducer. The gap height of our transducers is chosen to be slightly smaller than the static deflection of the plate due to the pressure difference between the ambient and the vacuum cavity. Thus, the plates are in contact with the bottom of the cavities even with no dc bias applied. The devices were fabricated based on the thick box process. High-temperature assisted direct wafer bonding technique was used to fabricate devices with such large cell size (radii ∼ 2000 μm) featuring low frequencies ∼100–150 kHz. Extensive acoustic characterization was performed to demonstrate the behavior of such CMUTs in terms of displacement profile, output pressure and acoustic pitch-catch response. A maximum sound pressure of ∼145 dB (SPL) at the transducer surface is measured at 240 V dc and 10 V ac with 100 cycles of burst signal. This is a great improvement from conventional CMUTs (with deeper gap height, operating at 55 kHz), which requires 350 V dc and 200 V ac in order to achieve an output pressure of 129 dB (SPL) at the transducer surface. The results presented in this paper demonstrate that operating CMUTs in permanent contact mode indeed enhances the device output pressure, and provides a good candidate for efficient ultrasonic transducers.