*Article* **P-N Junction-Based Si Biochips with Ring Electrodes for Novel Biosensing Applications**

#### **Mahdi Kiani 1,\*, Nan Du 1,\*, Manja Vogel 2, Johannes Ra**ff **2, Uwe Hübner 3, Ilona Skorupa 2, Danilo Bürger 1, Stefan E. Schulz 1,4, Oliver G. Schmidt 5 and Heidemarie Schmidt 1,3,\***


Received: 28 August 2019; Accepted: 2 October 2019; Published: 11 October 2019

**Abstract:** In this work, we report on the impedance of p-n junction-based Si biochips with gold ring top electrodes and unstructured platinum bottom electrodes which allows for counting target biomaterial in a liquid-filled ring top electrode region. The systematic experiments on p-n junction-based Si biochips fabricated by two different sets of implantation parameters (i.e. biochips PS5 and BS5) are studied, and the comparable significant change of impedance characteristics in the biochips in dependence on the number of bacteria suspension, i.e., *Lysinibacillus sphaericus* JG-A12, in Deionized water with an optical density at 600 nm from OD600 = 4–16 in the electrode ring region is demonstrated. Furthermore, with the help of the newly developed two-phase electrode structure, the modeled capacitance and resistance parameters of the electrical equivalent circuit describing the p-n junction-based biochips depend linearly on the number of bacteria in the ring top electrode region, which successfully proves the potential performance of p-n junction-based Si biochips in observing the bacterial suspension. The proposed p-n junction-based biochips reveal perspective applications in medicine and biology for diagnosis, monitoring, management, and treatment of diseases.

**Keywords:** biochips; impedance spectroscopy; electrical equivalent circuit; biomaterial; *Lysinibacillus sphaericus* JG-A12
