A temperature sensor that uses temperature-sensitive fluorescent dyes is developed. The droplet sensor has a diameter of 40 µm and uses 1 g/L of Rhodamine B (RhB) and 0.5 g/L of Rhodamine 110 (Rh110), which are fluorescent dyes that are dissolved in an ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate) to function as temperature indicators. This ionic liquid is encapsulated using vacuum Parylene film deposition (which is known as the Parylene-on-liquid-deposition (PoLD) method). The droplet is sealed by the chemically stable and impermeable Parylene film, which prevents the dye from interacting with the molecules in the solution and keeps the volume and concentration of the fluorescent material fixed. The two fluorescent dyes enable the temperature to be measured ratiometrically such that the droplet sensor can be used in various applications, such as the wireless temperature measurement of microregions. The sensor can measure the temperature of such microregions with an accuracy of 1.9 °C, a precision of 3.7 °C, and a fluorescence intensity change sensitivity of 1.0%/K. The sensor can measure temperatures at different sensor depths in water, ranging from 0 to 850 µm. The droplet sensor is fabricated using microelectromechanical system (MEMS) technology and is highly applicable to lab-on-a-chip devices.

Ethanol concentration was quantified by the use of a compact surface plasmon resonance (SPR) system, which electrically detects hot electrons via a Schottky barrier. Although it is well known that SPR can be used as bio/chemical sensors, implementation is not necessarily practical, due to the size and cost impediments associated with a system with variable wavelength or angle of incidence. However, scanning capability is not a prerequisite if the objective is to use SPR in a sensor. It is possible to build a small, inexpensive SPR sensor if the optics have no moving parts and a Schottky barrier is used for electrical current detection in place of a photodetector. This article reports on the design and performance of such a novel SPR sensor, and its application for quantifying ethanol concentration. As the concentration of ethanol is increased, the change in the angle dependence of the SPR current is observed. This change can be understood as a superposition of contributions of SPR coupled with the +3rd- and −3rd-order diffraction. Moreover, real-time monitoring of ethanol concentration was demonstrated using the proposed SPR system.

We propose an insertion force sensor with piezoresistors fabricated by sidewall-doping with rapid thermal diffusion. The sensor consists of a main body, to which a pointed tip is installed, and supporting beams whose sidewalls are made piezoresistive. When an insertion force is applied to the tip and the silicon structure deforms, the change of the strain distribution condition on the piezoresistive sidewall varies the electrical resistance of the sensor, which is in turn transduced into output voltage signal via an outside circuitry. The beams are 250 µ m in length, 20 µ m in thickness, 8 µ m in width. By etching an appropriate pattern onto the wafer, additional exposed surfaces for doping can be created where vertical dope-sites are needed. With rapid thermal diffusion, we are able to fabricate dope-sites which are perpendicular to the surface of the wafer. Fabricated piezoresistive sensor has 20 pairs of supporting beams. The spring constant is 2500 N/m. The electrical resistance is 1.6 kΩ. The displacement sensitivity is 1.03 % per µ m. This displacement sensitivity on the insertion direction is as high as that on the vertical direction of reported sensors, which means that our proposal is an effective doping method for sidewall.