Gold-on-glass microwave split-ring resonators with PDMS microchannels for differential measurement in microfluidic sensing

This paper describes a microwave resonator incorporating microfluidic lab-on-chip sensor system capable of performing simultaneous differential measurement based sensing of liquid samples. The resonators are split-ring resonator shapes made of gold on glass substrates. Directly bonded on glass substrates are polydimethylsiloxane microchannels. Sensor system design incorporates a pair of identical resonators, one of which performs reference reading from the background. Tracking the difference of the responses of both resonators simultaneously, rather than a single one, is used to obtain a more linear and noise-free reading. The sensor system was produced with conventional fabrication techniques. It is compatible with low-cost, simple, easy to handle sensing applications. Results indicate that reliable differential measurement was possible owing to a well-matched pair of sensors with a response error as low as 0.1%. It was also demonstrated that differential measurement capability enables sensing with improved linearity. Measurements were performed with glucose solutions in the range of 3.2-16.1 mM, achieving a sensitivity of 0.16 MHz/mM.

Integrated sensing layer of bacterial cellulose and polyethyleneimine to achieve high sensitivity of ST-cut quartz surface acoustic wave formaldehyde gas sensor

Surface acoustic wave (SAW)-based formaldehyde gas sensor using bi-layer nanofilms of bacterial cellulose (BC) and polyethyleneimine (PEI) was developed on an ST-cut quartz substrate using sol-gel and spin coating processes. BC nanofilms significantly improve the sensitivity of PEI films to formaldehyde gas, and reduces response and recovery times. The BC films have superfine filamentary and fibrous network structures, which provide a large number of attachment sites for the PEI particles. Measurement results obtained using in situ diffuse reflectance Fourier transform infrared spectroscopy showed that the primary amino groups of PEI strongly adsorb formaldehyde molecules through nucleophilic reactions, thus resulting in a negative frequency shift of the SAW sensor due to the mass loading effect. In addition, experimental results showed that the frequency shifts of the SAW devices are determined by thickness of PEI film, concentration of formaldehyde and relative humidity. The PEI/BC sensor coated with three layers of PEI as the sensing layer showed the optimal sensing performance, which had a frequency shift of 35.6 kHz for 10 ppm formaldehyde gas, measured at room temperature and 30 % RH. The sensor also showed good selectivity and stability, with a low limit of detection down to 100 ppb.

Miniaturized magnetic bead-actuators for force-clamp spectroscopy-based single-molecule measurements

Force-clamp spectroscopy can mimic the physiological conditions for the proteins under investigation. In addition, it is a direct way of observing the relationship between bond lifetime and molecular forces. However, traditional force-clamp methods rely on active feedback controllers that can introduce artefacts. In this work, we introduce a new method to enable force-clamp spectroscopy without a need for an active feedback. The method is based on miniaturized magnetic beads offering improved stability. As a case study, we performed force-clamp experiments using biotin-streptavidin molecule pairs with and without active feedback. Our results demonstrate the feasibility of force-clamp experiments without feedback and illustrate the advantages of our method.

Note: Tunable overlapping half-ring resonator

A unique tunable microwave resonator with a pair of half-rings is introduced and validated by experimental data. The capacitive gap between the overlapping areas can be controlled accurately using a magnetic actuator for tunability. The design geometry is scalable to cover different bands of electromagnetic spectrum. Transmission characteristics of the resonators have been modeled using finite-element analysis and have been measured. The experimental results indicate the resonant frequency can be controlled with a resolution of a few MHz in a tuning range of 38%. The resonator exhibits sharp transmission dips within the tuning range with measured quality factors larger than 2500.

Note: Seesaw actuation of atomic force microscope probes for improved imaging bandwidth and displacement range

The authors describe a method of actuation for atomic force microscope (AFM) probes to improve imaging speed and displacement range simultaneously. Unlike conventional piezoelectric tube actuation, the proposed method involves a lever and fulcrum "seesaw" like actuation mechanism that uses a small, fast piezoelectric transducer. The lever arm of the seesaw mechanism increases the apparent displacement range by an adjustable gain factor, overcoming the standard tradeoff between imaging speed and displacement range. Experimental characterization of a cantilever holder implementing the method is provided together with comparative line scans obtained with contact mode imaging. An imaging bandwidth of 30 kHz in air with the current setup was demonstrated.

Athermalization in atomic force microscope based force spectroscopy using matched microstructure coupling

The authors describe a method for athermalization in atomic force microscope (AFM) based force spectroscopy applications using microstructures that thermomechanically match the AFM probes. The method uses a setup where the AFM probe is coupled with the matched structure and the displacements of both structures are read out simultaneously. The matched structure displaces with the AFM probe as temperature changes, thus the force applied to the sample can be kept constant without the need for a separate feedback loop for thermal drift compensation, and the differential signal can be used to cancel the shift in zero-force level of the AFM.