Since the working mechanism of triboelectric nanogenerators (TENGs) is based on triboelectrification and electrostatic induction, it is necessary to understand the effects of the inherent properties of dielectric materials on the performance of TENGs. In this study, the relationship between the relative permittivity and the performance of TENGs was demonstrated by fabricating TENGs using both pure oxide materials (SiO₂, Al₂O₃, HfO₂, Ta₂O₅ and TiO₂) and oxide–PMMA composites. As oxide materials and PMMA are triboelectrically positive, PTFE film was selected as the counter tribo-material, which has highly negative triboelectric polarity. The triboelectric series of the above-mentioned oxides was experimentally organized to clarify the major parameter for the performance of TENGs. The electrical data values for both oxides and composites clearly showed a tendency to increase as the relative permittivity of the tribo-material increased. It is also well-matched with the theoretical analysis between the electrical performances (e.g. open-circuit voltage) and relative permittivity. However, such a tendency is not observed with the triboelectric polarity. Due to the tribo-material’s high relative permittivity, an open-circuit voltage of 124.1 V, a short-circuit current of 14.88 μA and a power of 392.08 μW were obtained in a pure TiO₂ thin film.

This paper presents the first CMOS Vascular Endothelial Growth Factor (VEGF) sensor for cancer diagnosis directly from human blood. The sensor incorporates a peptide aptamer-based microneedle that allows the detection of electrochemical reactions with VEGF. This results in a capacitance change between the microneedles and then reads out by a two-step capacitance-to-digital converter (CDC). The proposed two-step CDC consists of a coarse 5b slope ADC and a fine 14b continuous-time delta-sigma modulator (CTDSM). During slow peptide-binding, the slope ADC performs a coarse conversion and the results are used to adjust the current level of the stimulator. After settling of the peptide-binding, based on an adjusted stimulation current, the CTDSM measures the small capacitance changes of the sensor. The prototype chip is fabricated in a 65-nm CMOS process, occupying a 0.87 mm2 active area. The power consumption is 270 W. Thanks to the two-step approach, this work achieves a wide dynamic range of 18.3b, covering a large sensor-to-sensor variation. It also achieves a peak resolution of 13.7b, while maintaining <0.02% errors in 1 to 100 nF baseline capacitance. The overall sensor system successfully detects the VEGF in both phosphate-buffered saline (PBS) and human blood serum. Without the use of precision instruments, this work achieves a resolution of 15 fMrms in range of 0.1 to 1000 pM and denotes the clear VEGF selectivity at 40× in PBS and 5× in the blood serum compared to other proteins (IgG, Con A, and cholera toxin).