Facilitated biosensing via direct electron transfer of myoglobin integrated into diblock copolymer/multi-walled carbon nanotube nanocomposites
Nanocomposite materials were prepared by sequential drop-casting of multi-walled carbon nanotube (MWCNT) suspensions and amphiphilic polybutadiene-block-poly(2-(N,N-dimethylamino)ethyl methacrylate) (PB290-b-PDMAEMA240) diblock copolymer micellar solution on screen-printed electrodes (SPEs). These nanocomposite materials were found to be very favorable for integration of myoglobin (Mb) and facilitate direct electron transfer from the electrodes to heme proteins. In that respect, PB290-b-PDMAEMA240 was demonstrated to be a well-suited binding agent. In aqueous solutions, it forms core–corona micelles (shown by cryogenic transmission electron microscopy, cryo-TEM, and nanoparticle tracking analysis, NTA), which at pH 7 in phosphate buffer exhibit good adhesion to carbon materials (shown by atomic force microscopy, AFM, scanning electron microscopy, SEM, and scanning transmission electron microscopy, STEM) and build up uniform thin films on a hydrophobic graphite-based substrate. As demonstrated by a quartz crystal microbalance with dissipation monitoring, QCM-D, attractive interactions between Mb and PB290-b-PDMAEMA240 take place when both components are subsequently deposited onto a solid substrate. Spectroscopic studies confirmed that the absorption maximum of Mb remains unaltered, suggesting that at least some protein globules retain their tertiary structure. Cyclic voltammetry, CV, and square wave voltammetry, SWV, show a remarkable (ca. 180-fold) increase of the reductive current of Mb after its incorporation into the SPE/MWCNT/PB290-b-PDMAEMA240 matrix. The herein developed analytical approach was used for the detection of cardiac myoglobin as a very early marker of acute myocardial infarction (AMI) both in plasma of healthy donors and patients with AMI.