ABSTRACT
Microfluidic sensors possess several advantages such as smaller sample volume, shorter assay time, and lower cost compared with conventional assays performed in 96-well plates. However, because of its miniaturized format, microfluidic sensors also face serious challenges in signal detection because of the inherent short light path length, small sample volume, and short residence time. To overcome these limitations in microfluidic sensors, ultrasensitive signal detection and amplification mechanism are often required. In the past, laser-induced fluorescence (LIF) detection and enzymatic signal enhancement were the preferred detection methods in microfluidic sensors because of their high sensitivity. In these methods, target molecules need to be conjugated with labels such as fluorophores (Bernard et al. 2001; Hosokawa et al. 2007), enzymes (Eteshola and Balberg 2004; Yu et al. 2009); nanoparticles (Lu et al. 2009; Luo et al. 2005), and redox labels (Lim et al. 2003) to transduce detection signals. Nevertheless, labeling target molecules is tedious and the functionality of the molecules can be compromised upon conjugation with labels (Shrestha et al. 2012; Thorek et al. 2009). More importantly, if bulky instruments such as laser and fluorescence detectors are needed, then it becomes very difficult to miniaturize these microfluidic sensor devices. A better sensing mechanism fully compatible with a microfluidic device is therefore needed.
