Effect of dendrimer-based interlayers for enzyme immobilization on a model electrochemical sensing system for glutamate.

In this paper, we discuss dendrimer usage in enzyme-based electrochemical biosensors, particularly with respect to biomolecule loading on the sensing surface. A novel approach to design bioactive layers with immobilized enzymes for electrochemical biosensors using the surface plasmon resonance (SPR) method in combination with electrochemical impedance spectroscopy was presented. The gold surface was modified with linear linkers (various mercaptoalkanoic acids and aminoalkanethiols) and poly(amidoamine) dendrimers from the first- to fifth-generation. The best functionalization procedure was established by detailed SPR studies and transferred onto gold electrodes to electrochemically examine the model enzymatic reaction catalysed by glutamate oxidase. In the case of the chronoamperometric method, the determined sensitivity was 3.36 ± 0.08 µA∙mM-1, and the low limit of detection (LOD) was 1.52 µM. Comparing the sensitivity and LOD obtained for CV measurements, the values of these parameters were 2.5 times higher and 4 times lower, respectively, for the fourth-generation dendrimer-based biosensor and the biosensor with a linear linker. The positive impact of the dendrimer interlayer on the long-term enzyme activity was also confirmed. The research results indicate the possibility of a significant increase in the sensor response using the dendrimer itself without enriching it with electrochemical components.

Optimization of a PVC Membrane for Reference Field Effect Transistors.

For the miniaturization of ISFET sensing systems, the concept of a REFET with low ion sensitivity is proposed to replace the conventional reference electrodes through the arrangement of a quasi reference electrode and a differential readout circuit. In this study, an ion-unblocking membrane was used as the top layer of a REFET. To optimize the REFET performance, the influences of the silylating process, different plasticizers, and the composition of the PVC cocktails were investigated. A low sensitivity (10.4 ± 2.2 mV/pH) and high linearity (99.7 ± 0.3 %) in the range from pH 2.2 to pH 11.6 was obtained for the REFET with a 60 wt.% DNP/(DNP + PVC) membrane. To evaluate the long term stability, the drift coefficient was estimated, and for the best REFET, it was -0.74 mV/h. Two criteria for assessing the lifetime of REFETs were used, namely the increase in pH sensitivity to a value higher than 15 mV/pH and the degradation of linearity below 99 %. For the best REFET, it was approximately 15 days.