Tremendous demands for sensitive and reliable label-free biosensors have stimulated intensive research into developing miniaturized radiofrequency resonators for a wide range of biomedical applications. Here, we report the development of a robust, reusable radiofrequency resonator based integrated passive device biosensor chip fabricated on a gallium arsenide substrate for the detection of glucose in water-glucose solutions and sera. As a result of the highly concentrated electromagnetic energy between the two divisions of an intertwined spiral inductor coupled with an interdigital capacitor, the proposed glucose biosensor chip exhibits linear detection ranges with high sensitivity at center frequency. This biosensor, which has a sensitivity of up to 199 MHz/mgmL−1 and a short response time of less than 2 sec, exhibited an ultralow detection limit of 0.033 μM and a reproducibility of 0.61% relative standard deviation. In addition, the quantities derived from the measured S-parameters, such as the propagation constant (γ), impedance (Z), resistance (R), inductance (L), conductance (G) and capacitance (C), enabled the effective multi-dimensional detection of glucose.

A bandpass filter (BPF) with a central frequency of 2.31 GHz for future worldwide interoperability for microwave access (WiMax) applications using integrated passive device technology is presented. To realise the BPF, an interdigital capacitor is integrated between the two divisions of a square-shaped spiral inductor. To achieve a compact size, the capacitor is fully embedded inside the inductor. Additionally, the coils of the inductor are intertwined to utilise enhanced mutual inductance for minimising the loss of signal transmission. The strong electromagnetic coupling between the source and load through the interdigital capacitor results in excellent bandpass skirt selectivity with a measured return loss of 26.1 dB. Moreover, it provides an improved stopband response due to the presence of a transmission zero at 5.94 GHz.Introduction: With the rapid development of worldwide interoperability for microwave access (WiMax) systems, the demand for compact bandpass filters (BPFs) with high performance and high integration is increasing quickly. To fulfil this demand, integrated passive device (IPD) processes have been widely utilised to implement BPFs [1, 2] with various design approaches, because they provide the advantages of mass production of devices with more reliable performance than other passive technologies. The BPF previously realised with a suspended spiral inductor on an anodised aluminium oxide has a compact size and a high-quality factor inductor [1]. However, its insertion and return losses require improvement. In [2], two coupled spiral inductors are integrated on an Al 2 O 3 substrate to obtain a compact BPF, which also suffers from high insertion loss. Therefore, the design of a BPF with a more compact size and excellent skirt selectivity is desirable.In this Letter, we present a BPF based on a combination of a squareshaped spiral inductor and an interdigital capacitor (IDC) with the objectives of miniaturised size and high selectivity. To verify the proposed concept, a protocol BPF with a simulated central frequency of 2.31 GHz has been fabricated on GaAs substrate. The measured insertion and return losses of 0.8 and 26.1 dB, respectively, at the central frequency, show that the fabricated filter exhibits excellent passband selectivity. Additionally, a transmission zero (TZ) located at 5.94 GHz in the stopband region of the filter suppresses the signal by more than 34 dB to generate a wide stopband response.

Passive sensors provide a new route for the characterization of concentration-dependent radiofrequency parameters with high reproducibility in real time.

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