Nitride devices and their biofunctionalization for biosensing applications
The past two decades have witnessed considerable interest in biosensor development. The heart of these hybrid analytical devices is the immobilized biologically sensitive material integrated within a transducer. A biosensor ultimately converts the biological information into a quantitatively measurable signal, usually in the form of optical, acoustic, electrical, or magnetic responses. In the realm of biosensors, semiconductor-based devices constitute a promising alternative for molecular detection based on high-sensibility responses in electron transfer, adsorption, surface recombination, photoconductivity, and light-induced contact potential measurements.
Next-generation affinity-based biosensors will require significant improvements in sensitivity, specificity, and parallelism in order to meet future needs in a variety of fields, including in vitro medical diagnostics, pharmaceutical discovery, and drug and pathogen detection. The interface between biological molecules and semiconductor surfaces is a key issue in the development of efficient devices based on biomolecular recognition.
The use of high-sensitivity semiconductor materials such as nitrides can considerably enhance biosensing performances. For example, indium nitride (InN) has proven to have robust surface properties and unusually strong surface- electron accumulation, and gallium nitride (GaN) reveals outstanding chemical stability and is transparent, enabling easy optical readout, rendering nitrides as very promising substrates for biological detection. In terms of interfacing them with biological materials, nitrides also present the advantage of a relatively easy functionalization due to their affinity to various organic linkers. Nitrides can be selectively functionalized with peptides produced by a biotechnological method called “phage display”, which can be crucial when the retention of contrast in multi-material components is necessary. Biomolecules’ capturing can be electrically or optically monitored by metal semiconductor field-effect transistors or photonic crystal resonances, respectively. Photonic crystals provide strong light confinement and can be designed to localize the electric field in the low-refractive- index region, which makes the sensors extremely sensitive to a small change of refractive index produced by the biomolecular binding event. Moreover, their nanostructured design makes them ideal candidates for the development of miniaturized biosensors with very low requirements in terms of volume of biological material.