The electrical contact may become unstable, especially for the detections that require repeated probing on the same gold electrodes. For instance, electrochemical detection of deoxyribonucleic acid (DNA) hybridization usually needs two time measurements, before and after the hybridization process in an oven at an elevated temperature.Several probing methods have been utilized for the contact on gold electrodes [12�C14]. A conductive adhesive such as silver paste may provide stable contact connecting to a potentiostat only for one time probing of electrochemical measurements, but probing with a conductive adhesive is destructive once it is hardened. A needle-like probe or an alligator clip can be a better method for multiple measurements as they work by physical contact. However, there is still the issue of the potential destruction of the gold electrode due to scratching or tearing by shear force when the experiment requires alternating attachment and detachment processes.In this article, we demonstrate how electrochemical measurement is affected by the deformation of gold electrode and suggest a novel probing method, the universal spring-probe system, which provides repeated multiple stable contacts, enabling a consistent electrochemical detection throughout experiments. The practicality of the universal spring-probe system will be specifically demonstrated in the detection of DNA hybridization that needs two measurements before and after hybridization.2.?Experimental Section2.1. Fabrication of the Spring-Probe SystemThe two parts of the spring-probe system, the top cover and bottom case, were made of cyclic olefin copolymer (COC). The flat COC plate (80 �� 80 mm, 5 mm thick) of the top cover was drilled using a computer numerical control machine (TinyCNC-6060C, Tinyrobo, Bucheon, Korea) to make 0.9 mm holes for the spring-probes (G070R, Leeno Industrial Inc., Busan, Korea). The resistance of the spring-probes is less than 50 m?. Spring-probes were inserted into the holes and then firmly attached by instant adhesive or fixed by rubber rings. A rectangular (60 �� 60 mm, 6 mm deep) crater was processed in another flat COC plate (80 �� 80 mm, 10 mm thick) for the bottom case to set the LOC in.2.2. Fabrication of the LOCThe LOC was composed of three COC plates (60 �� 60 mm, 1 mm thick) that were formed by an injection mold machine (A270C400-100, Arburg GmbH, Lobburg, Germany). The lower one was a flat COC plate. The middle one had open areas for probing, energy directors for ultrasonic welding and inlet and outlet structures. The upper one also had open areas for inlet, outlet and probing. For electrode patterning, gold (200 nm) with chromium (20 nm) as adhesion layer were deposited on the lower COC plate with shadow mask using an evaporator (EBS400, Evatec, Flums, Switzerland).selleckchem Wortmannin Double-side adhesive polyimide film (60 �� 60 mm, 0.2 mm thick) was utilized to form the microfluidic channels as well as to bond the lower and middle plates.