Integration of localized surface plasmon resonance and electrochemical sensors for liquid environmental monitoring

Simultaneous measurements of several properties are important for a microfluidic system application. In this paper, electrochemical and localized surface plasmon (LSPR) sensors were integrated on an interdigital electrode (IDE) for simultaneous monitoring of impedance and refractive index of samples. First, the IDE was made and then gold nanoparticles were formed on the IDE electrodes by the thermal annealing method for the LSPR sensor. The measured results suggest that the electrical and optical properties of samples are measurable by the integrated IDE.

I. Introduction

Integration of several sensors on one device is important for simultaneous detections of several properties. We have investigated digital microfluidic system (DMFS) based on a surface acoustic wave (SAW) device [1] . Fig. 1 shows the conceptual figure of the DMFS using the SAW device. Droplets are manipulated and mixed by the SAW, which is generated from the interdigital transducer (IDT). The droplet manipulation mechanism is based on the SAW streaming [2 , 3] . The longitudinal wave is radiated from the SAW and the acoustic streaming is caused by the radiated longitudinal wave, when the amplitude of the SAW is larger than the threshold value. The acoustic streaming is the nonlinear phenomenon. As the amplitude of the SAW is proportional to the electrical-signal amplitude applied to the IDT, the phenomena are controlled by the electrical signal. First, vortices are observed in the droplet (see Fig. 2 [4] ). Then, droplet manipulation, small droplet ejection from a droplet, and atomization [5] . Also, the temperature control of a droplet is possible [6] . Therefore, the SAW device has high potential for the DMFS application, if an optimum sensor is integrated on it.