In this work, we describe a new sensor that specifically responds to biothiols, i.e., glutathione (GSH), in solution. An electrochemical transducing strategy was utilized and cyclic voltammetry (CV) was employed to monitor the presence of GSH in real time. Our approach harnessed self-assembled monolayers (SAMs) on gold consisting of an alkanethiolate which was terminated by electroactive quininoid moiety. Prior to thiol molecule treatment, the characterisitc reversible redox peaks of the electroactive quininoid group was observed, while the reduction peak was dramatically shifted upon a treatment of GSH. This sensor showed the capability to detect the GSH in solution in the range of 1 mM $sim$ 100 aM. We believe that this strategy will provide an important tool for accurate, sensitive, rapid, and low-cost determination of GSH.