Electrospinning-based nanobiosensors

Abstract

Biological interactions in biosensors occur through different mechanisms, on the basis of the type of biological receptor elements employed therein that confer the biological specificity to the biosensors themselves (biocatalytic, biocomplexing or bioaffinity biosensors). The use of different transduction systems (amperometric, potentiometric, field-effect transistors, piezometric and conductometric) defines the mode of detection. The interest and relevance of nanomaterials in the fabrication of nanobiosensors lie in their extraordinary properties that make them ideally suited and very promising for sensing applications. The resulting nanobiosensors are capable of sensing analytes in traces with fast, precise and accurate biological identification through miniaturised and easy to use systems. These advanced sensors are also characterised by lower detection limits, higher sensitivity values and high stability, and can further offer multi-detection possibilities. These exceptional features make nanobiosensors as the favourite tools in quality control, food safety, and traceability for their capacity of revealing and warning people against the presence of pathogens, toxins and pollutants, as well as bioterrorism agents. Despite the outstanding properties of these nanobiosensors, however, the efficiency of the biorecognition agent and the number of biorecognition sites available for interacting with target analytes can limit the sensitivity of this kind of sensors. The number of available biorecognition sites is directly related to the surface area of the sensor. Electrospinning technology can significantly increase the sensitivity of biosensors by replacing the typical planar interactive surface of conventional biosensors with a mat of electrospun nonwoven nanofibres, thereby taking advantage of the ultrahigh surface area offered by electrospun nanofibres. Moreover, adjusting the electrospinning process to produce hollow nanofibres can further increase the surface area of electrospun nanofibres. The immobilisation of bioreceptors into or onto electrospun nanofibres remarkably increases the number of recognition sites for biosensing, i.e. available for capturing the analytes through specific binding mechanisms. Furthermore, electrospinning technology can provide the deposition onto transducers of 3D frameworks of electrospun nanofibrous mat, with a tunable interconnected porosity, predictable pore geometries and sizes, and large global pore volumes. Such feature can supply further properties to the resulting nanobiosensor suitable for the detection of analytes in particular environments, where an efficient transport of the analytes through the membrane toward the electrode surface is required. Due to such an extreme versatility, electrospinning is expected to have several strategic advantages over other nanotechnologies as concerns nanobiosensing. In the present chapter, a brief overview of the main recent studies on electrospun nanobiosensor and applications is proposed. Attention is focused on enzyme-based nanobiosensors, and the advantages and drawbacks of enzyme immobilisation as well as improvements due to employment of electrospinning in these biosensors are presented. Specifically, the application of nanobiosensors in glucose detection and the contribution of electrospinning to these sensing systems are reported. Furthermore, the use of bioaffinity mechanisms in recognition processes of nanobiosensors is considered by focusing on nanobiosensors employing hybridisation probes and functional nucleic acids (aptamers, peptide nucleic acids, Rybozymes, DNAzymes and Aptazymes) and their outstanding sensitivities are described. The improvements of electrospinning in these sensing systems are highlighted, when applicable. Similarly, electrospun-based immunobiosensors (antibody-based nanobiosensors) and their applications are described.