Soft and flexible material-based affinity sensors

Abstract

Recent advances in biosensors and point-of-care (PoC) devices are poised to change and expand the delivery of diagnostics from conventional lateral-flow assays and test strips that dominate the market currently, to newly emerging wearable and implantable devices that can provide continuous monitoring. Soft and flexible materials are playing a key role in propelling these trends towards real-time and remote health monitoring. Affinity biosensors have the capability to provide for diagnosis and monitoring of cancerous, cardiovascular, infectious and genetic diseases by the detection of biomarkers using affinity interactions. This review tracks the evolution of affinity sensors from conventional lateral-flow assay and test strips to wearable/implantable devices enabled by soft and flexible materials. Initially, we highlight conventional affinity sensors exploiting membrane and paper materials which have been so successfully applied in point-of-care tests, such as lateral-flow immunoassay strips and emerging microfluidic paper-based devices. We then turn our attention to the multifarious polymer designs that provide both the base materials for sensor designs, such as PDMS, and more advanced functionalised materials that are capable of both recognition and transduction, such as conducting and molecularly imprinted polymers. The subsequent content discusses wearable soft and flexible material-based affinity sensors, classified as flexible and skinmountable, textile materials-based and contact lens-based affinity sensors. In the final sections, we explore the possibilities for implantable/injectable soft and flexible affinity sensors, including hydrogels, microencapsulated sensors and optical fibers. This area is truly a work in 2 progress and we trust that this review will help pull together the many technological streams that are contributing to the field.

Tailoring Conducting Polymer Interface for Sensing and Biosensing

“…Among the soft and flexible materials, conducting polymers (CPs) have attracted tremendous interest and have developed rapidly in both the academic and industrial communities. Desirable organic polymer characteristics such as well-maintained flexibility and structural diversity, and newly introduced electronic/ionic conductivity and redox reversibility by a doping/de-doping process, make them well suited for applications in electrochemistry-related applications, such as energy and biomedical devices 5 . In addition, the similarities of CPs in their organic nature with biological molecules facilitates the concept of organic bioelectronics (OBEs), bridging the world of organic electronics in CPs with bioelectronics in biological systems 6 .…”

Bi-functional sulphonate-coupled reduced graphene oxide as an efficient dopant for a conducting polymer with enhanced electrochemical performance

“…6 To enhance the performance of the CPs for electrochemical signal transduction, various nanomaterials in different dimensional architectures with unique physical-chemical properties, such as carbon-based nanomaterials, metal/metal oxide nanoparticles, dyes, etc., have been incorporated into the CP matrix as negatively-charged dopants integrated to the positivelycharged CP backbone during the polymerisation process. 7 The incorporation of these nanomaterials endow CPs with enhanced or even extended electrochemical properties owing to synergistic effects such as increased active surface area, enhanced charge/electron transfer and improved mechanical stability. [6][7][8] In the meantime, doping of CPs with other materials also brings in less-control of bulky surface morphology with fragile mechanical property, surface defects and non-uniform distribution, especially for large dopant.…”

“…7 The incorporation of these nanomaterials endow CPs with enhanced or even extended electrochemical properties owing to synergistic effects such as increased active surface area, enhanced charge/electron transfer and improved mechanical stability. [6][7][8] In the meantime, doping of CPs with other materials also brings in less-control of bulky surface morphology with fragile mechanical property, surface defects and non-uniform distribution, especially for large dopant. 9,10 To realise CP composites with high conductivity, uniform distribution of the nanomaterial within the composite and high polymerisation efficiency, several essential prerequisites for the dopant have to be fulfilled including an appropriate conductivity, aqueous dispersibility and colloidal stability, and the right functional groups.…”

Grand Challenges in Nanomaterial-Based Electrochemical Sensors

“…When using nanomaterials, long-term stability might become a major concern due to issues related to aggregation and flaking of nanomaterialmodified layers. Recently, incorporation of sol-gel materials and ceramics along with nanomaterials has been proven to increase the stability of sensors (Kim et al, 2018;Li et al, 2019;Meng et al, 2020). Moreover, designing sensors that are stretchable, self-healing, water-processable and wearable has recently been a major advancement in the sensing field (Kim et al, 2018;Li et al, 2019;Meng et al, 2020).…”

“…These types of miniaturized sensors, which have great stability, are often made with rubber-like composites, hydrogels, organogels and novel polymers. Combining these highly stretchable materials with the excellent electrical conductivity of nanomaterials makes for remarkable sensors with superior analytical performance characteristics (Kim et al, 2018;Li et al, 2019;Meng et al, 2020).…”