We report a label-free porous silicon membrane waveguide biosensor based on a 1μm thick freestanding porous silicon film with 100nm diameter pores. The sensor operates in the Kretschmann configuration. A formvar polymer film provides robust adhesion of the porous silicon membrane to a rutile prism and enables confinement of guided modes in the porous silicon membrane. Attenuated total reflectance measurements are performed, along with theoretical calculations, to fully characterize the waveguide. The sensitivity of the sensor is investigated through DNA hybridization in the porous silicon membrane. A detection limit of 42nM was demonstrated for 24-base pair DNA oligonucleotides.
Continuous drug monitoring is a promising alternative to current therapeutic drug monitoring strategies and has strong potential to reshape our understanding of pharmacokinetic variability and to improve individualised therapy. This review highlights recent advances in biosensing technologies that support continuous drug monitoring in real time. We focus primarily on aptamer-based biosensors, wearable and implantable devices. Emphasis is given to the approaches employed in constructing biosensors. We pay attention to sensors’ biocompatibility, calibration performance, long-term characteristics stability and measurement quality. In the end, we discuss about the current challenges and issues to address in continuous drug monitoring to make it a promising, future tool for individualised therapy. The ongoing efforts are expected to result in fully integrated implantable drug biosensing technology. Thus, we may anticipate an era of advanced healthcare in which wearable and implantable biochips automatically adjust drug dosing in response to patient health conditions enabling the management of diseases and enhancing individualised therapy.
1 Introduction Porous materials are increasingly employed in biosensing applications, primarily because of two important characteristics: a large available surface area to immobilize more probe biomolecules than is feasible on a planar surface, and the capability to selectively exclude larger-sized non-specific biomolecules from the sensor active region in which false positives could result. Several types of biosensors utilizing porous materials have been reported, including biosensors based entirely on a porous material, such as porous silicon [1 -5], and structures employing porous materials to enhance the performance of existing biosensors, such as optical waveguide sensors enhanced with porous TiO 2 [6] or a perforated silica film [7], surface plasmon resonance sensors enhanced with mesoporous silica [8], surface acoustic wave sensors enhanced with a porous resin [9], and optical fiber sensors enhanced with a sol-gel coating [10]. Due to the small pore size of many of these enhanced sensors, gas detection has been the foremost application of sensors utilizing porous materials. For biosensing applications, the porous sensors are limited to the detection of molecules smaller than the pore diameter. However, at nanoscale dimensions, it is not obvious what minimum pore-size-to-biomolecule-size
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