## 1 Introduction  
The detection and quantification of cells in complex samples remains a challenge and an important issue for applications such as medical diagnosis and food safety. For medical diagnosis, the detection of cancer cells and pathogenic bacteria cells in the blood is utilized to diagnose disease. The detection of circulating tumor cells (CTCs) in the blood has been shown to be clinically important for early stage metastasis or the recurrence of cancer. The presence of rare CTCs in the blood ranges from only 1 to 100 CTCs/mL blood [1]. _Plasmodium falciparum malaria_--which mainly kills children in developing countries--infects the blood of patients at a concentration of ~1/50 \(\mu\)L of blood [2]. Regarding food safety, the contamination of drinking water or wastewater with microorganisms such as _E. coli_ and _Salmonella_ has been a serious issue for several developing countries [3]. As those bacteria can multiply rapidly, it is necessary to detect them quickly, easily, and inexpensively. In order to meet the requirements for these applications, the platforms need to be rapid, sensitive, and cost-efficient. The classical method for cell detection in suspension is through the use of flow cytometry, which is a rapid and highly accurate measurement technique. This technique--first reported by [PERSON] [4]--has emerged in microfabricated devices in order to analyze microscale particles with high sensitivity. For instance, colloids as small as 87 nm could be detected by a microchip Coulter counter on a quartz substrate [5]. However, flow cytometry has high manufacturing cost and involves the labelling of cells with fluorescent antibodies [6]. Recently, impedance flow cytometry (IFC) has gained attention as a significant promising technique to replace and overcome the limitations associated with flow cytometry. IFC is preferable because it is a fast, real-time, and non-invasive method for biological detection. This technique can be utilized in cell counting [7], cancer cell detection [8], and bacteria detection [9]. Some groups have demonstrated detection and counting of cells by using a microfluidic integrated with an electrode for various electrical measurement methods for the applications of food safety [10] and real-time monitoring of bio-threats [11]. This measurement technique is based on the alteration of impedance across measurement electrodes due to the decreasing of ionic current passing between electrodes when a cell is present. IFC is capable of distinguishing and counting lymphocytes, monocytes, and neutrophils in whole human blood [7]. The concentration of spermatozoa in semen also causes a change in impedance when passing the electrodes [12]. Other studies reported that IFC can detect the presence of cells based on probing the impedance inside the cell at a frequency greater than 1 MHz [13]. A fabricated nanoneedle probe inside a microfluidic was utilized to measure the presence of cells at the sensor surface, making it sensitive to the dielectric properties of solution [14]. However, this device requires patterning of the electrode or probe on the substrate, resulting in higher cost of the fabrication process. Another limitation is the time-consuming cleaning process of the device. Several groups have demonstrated that the technique reduces the cost of microfabrication of electrodes by using printed circuit board (PCB) as a measurement electrode. They demonstrated contactless conductivity detection in a capillary electrophoresis environment [15] and contactless cell manipulation using dielectrophoresis [16]. Recently, contactless impedance cytometry was developed to reduce the fabrication cost of an impedance cytometry device [17; 18]. The electrode was fabricated on a PCB substrate (reusable component), and the thin bare dielectric substrate bonded to a PDMS (Polydimethylsiloxane) microchannel (disposable component) was placed onto PCB substrate. The sensitivity of this device is a limitation, since the electric field is buried in a dielectric substrate and does not reach the electrolyte.