Portable EIS and SERS sensing with flexible sensors

To debottleneck the core development of portable sensing, in this dissertation low-cost, highly sensitive sensors for impedance sensing and surface-enhanced Raman sensing have been designed and tested with mass-manufacturing ability. Starting from silicon-based through-hole impedance with a pre-concentrating function, 100 cells per milliliter detection limit has been achieved. In the following dissertation, the difficult-to-fabricate silicon sensor was replaced by a filter-based sensor, combining with a 3D printed scaffold and low-melting 3D printed filament confining the microfluidic channel, not only the cost was reduced significantly, but the detection limit was further improved by 20 times in the study using the Hook effect and improvement of the equivalent circuit model for paper-based impedance sensing. Further, we developed a Bluetooth-based impedance sensing component that can be used with a smartphone to work with this sensor easily. On the other hand, we have developed a wafer scale, flexible, polymer-based nano-pillar SERS sensor with an enhancement factor (EF) as high as 4.81 × 108 for the silver-based sensor. This high EF resulted from better adhesion between the substrate and detecting target, as well as the extended hotspots from the dense silver nanoparticles along the nano-pillars. Furthermore, in the following work, we also increased the EF by 3.4 times for a gold-coated sensor which is more stable, and bio-compatible by fine-tuning the distance among nano-pillars. With this ultrasensitive, low-cost, and highly uniformed substrate, the application with a handheld Raman spectrometer for the detection of drugs in wine was also demonstrated