Impact of surface roughness on Dielectrophoretically assisted concentration of microorganisms over PCB based platforms Geeta Bhatt 1 & Rishi Kant 1 & Keerti Mishra 2 & Kuldeep Yadav 1 & Deepak Singh 2 & Ramanathan Gurunath 2 & Shantanu Bhattacharya 1,3 Published online: 17 April 2017 # Springer Science+Business Media New York 2017 Abstract This article presents a PCB based microfluidic plat- form for performing a dielectrophoretic capture of live micro- organisms over inter-digitated electrodes buried under layers of different surface roughness values. Although dielec- trophoresis has been extensively studied earlier over silicon and polymer surfaces with printed electrodes the issue of sur- face roughness particularly in case of buried electrodes has been seldom investigated. We have addressed this issue through a layer of spin coated PDMS (of various surface roughness) that is used to cover the printed electrodes over a printed circuit board. The roughness in the PDMS layer is generally defined by the roughness of the FR4 base which houses the printed electrodes as well as other structures. Possibilities arising out of COMSOL simulations have been well validated experimentally in this work. Keywords PDMS . PCB . Inter-digitated electrodes . DEP . E. coli 1 Introduction The advancements in Micro/Nano Systems (MEMS/NEMS) technology have always served as a tool for scaling down a variety of structures which may serve mechanical or electrical purposes. The scaling down process is of utmost significance in biological world as some of the biological entities match size-wise with the scaled down structures and features. Due to this scale down effect there has been a revolution in clinical detection technology which has provided many solutions. One example could be the sensitive detection of pathogens in var- ious food and water samples. There have been many strategies involved earlier through use of pre-concentration, selective recognition, molecular recognition, molecular identification etc. on single microchip platforms (Nayak et al. 2013). Dielectrophoresis (DEP) phenomena has been extensively used in microchip architectures for separating, concentrating, manipulating etc. of target samples from neutral solutions by use of non-uniform electric field. Further DEP force has been characterized very well numerically (Pohl 1951) and is found to depend on particle polarizability, dielectric properties of the particles and surrounding media and also particle size. In fact the average DEP force (Jones 1996), F DEP for a spherical dielectric particle flowing in a medium is expressed as: F DEP ¼ 2πr 3 ε o ε m Re K ω ðÞ ½ ∇ E rms j j 2 ð1Þ where, r is the radius of the particle, ε o is permittivity of free space, ε m is real part of the permittivity of medium, E rms is RMS electric field and K(ω) is Clausius-Mossotti factor (mea- sure of effective polarizability of the particle). Clausius-Mossotti factor is expressed as: K ω ð Þ¼ ε * p -ε * m   ε * p þ 2ε * m   ; ε * p i ¼ p; m ð Þ ¼ ε i - j σ i ε o ω ð2Þ Here, m&p refers to the medium and particle, ε is permit- tivity, σ is conductivity and ω is angular frequency of applied * Shantanu Bhattacharya bhattacs@iitk.ac.in 1 Microsystems Fabrication Laboratory, Department of Mechanical Engineering, Indian Institute of Technology, Kanpur, Kanpur, India 2 Chemistry Department, Indian Institute of Technology, Kanpur, Kanpur, India 3 Design Program, Indian Institute of Technology, Kanpur, Kanpur, India Biomed Microdevices (2017) 19: 28 DOI 10.1007/s10544-017-0172-5