A printed SWCNT electrode modified with polycatechol and lysozyme for capacitive detection of α-lactalbumin

The authors describe an electrochemical sensor for the breast cancer marker alpha-lactalbumin (alpha LA). It is based on the use of printed single-walled carbon nanotube (SWCNT) electrodes that were modified with polycatechol. Impedance-derived electrochemical capacitance spectroscopy (ECS) is applied for detection at an applied potential of -0.14 V vs. Ag/AgCl reference electrode. The electrode was prepared in a two-step process. First, a dispersion of SWCNTs was drop-cast onto the surface of a poly(ethylene terephthalate) substrate to act as the working electrode. Next, catechol was electrochemically polymerized on the SWCNTs, prior to the immobilization of lysozyme. The strong interaction between lysozyme and alpha LA induced changes in the redox capacitance which are detected by ECS. The latter shows the device to be capable of detecting alpha LA in the 20 to 80 ng.mL(-1) concentration range. The limit of detection is 9.7 ng.mL(-1) at an S/N ratio of 3. The device was used to detect alpha LA in human blood serum with good recovery results.