The biological sensing interface on the active area of a piezo transducer is responsible for the sensitivity, specificity, reusability, and reproducibility of these devices. Among the approaches used to functionalize piezo transducers, mixed self-assembled monolayers (MSAMs) are one of the most successful, given that they allow the obtaining of semi-crystalline molecular arrays and the arrangement of a bioreceptor on the surface. But, to deploy MSAMs on a substrate effectively, one must optimize and characterize the structural ratio between them and the bioreceptor. In this paper, we developed a molecular model of the interaction between Bovine Serum Albumin (BSA) and MSAMs-functionalized gold substrates. First, we evaluated the conditions for the functionalization of the substrates and found that a 50:1 16-mercaptohexadecaonic acid (MHDA) to 11 mercapto-1-undecanol (MUA) ratio produced the best features on the surface. We also evaluated the specific conditions to immobilize BSA on MSAMs (using the afore-established ratio) via Atomic Force Microscopy (AFM), and then on a 10[Formula: see text]MHz quartz crystal microbalance (QCM), and with the data obtained we concluded that a structural ratio of 0.005 (MSAM/BSA) is obtained when 1[Formula: see text][Formula: see text]M MHDA and 200[Formula: see text][Formula: see text]g/mL BSA were used, provided the most suitable conditions for the functionalization of a piezo transducer.

In recent years, researchers have taken to biosensors as effective tools for detection due to their portability, low-cost, fast response, and practicality. Piezoelectricity gave way to quartz crystal microbalances (QCM), of which high-frequency QCMs (HFF-QCM 100MHz) are still being researched. In this paper, we use DNA immobilization on a HFF-QCM via self-assembled monolayers (SAM) technique. Immobilization was initially verified with ATR-FTIR. Then, DNA was immobilized in real time on the HFF-QCM crystals. A variation in the phase of the signal suggests fixation of DNA to the surface, in accordance with ATR-FTIR results. A density of 629 ng/cm2 was computed. Also, a positive correlation between immobilized DNA and DNA concentration, and the appearance of a saturation point between 1 and 5 μM were shown after analysis of different DNA concentrations.

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