The change of electron transfer resistance was calculated using the following the equation: Rct = Rct(AP-P) − Rct(AP) , where Rct(AP-P) was the value of electron transfer resistance after penicillin G binding to anti-penicillin G in AP/gold/s-BLM/GC and Rct(AP) was the value of electron transfer resistance of AP/gold/s-BLM/GC in working solution.