Boiling is one of the most effective heat transfer methods due to its high heat transfer coefficient. Therefore, boiling heat transfer plays a very important role for various applications in many technological and industrial areas. However, a very complex mechanism of boiling, especially bubble nucleation, is still not sufficiently understood. On the other hand, numerous experiments have revealed the existence of soft domains that called nanobubbles at the solid-liquid interface. In this study, to investigate the influence of the solid-liquid interface nanobubbles on the bubble nucleation, an atomic force microscope (AFM) is used to characterize the morphology of nanobubbles. In order to separate the effect of wettability of a solid surface from that of surface structure, a very flat hydrophobic surface was prepared. 1H,1H,2H,2H-Perfluoro-n-octylphosphonic acid (FOPA) formed the interface of hydrophobic self-assembled monolayers (SAMs). As the result of AFM measurement, many nanobubbles about 100 nm in diameter and 30 nm thick are observed at the interface of the FOPA surface and the pure water. In addition, to prove the existence of gaseous phase, the heat conductance measurement by time-domain thermoreflectance method (TDTR) was introduced. TDTR is an ultrafast optical pump probe technique well suited for thermal measurement of thin films. It enables to resolve the thermal conductivity of the thin film and the thermal conductance of the interface. If nanobubbles are the gaseous phase, the big change of interface heat thermal resistance will be seen and the TDTR signal should also change. The effectiveness of a TDTR to confirm the existence of nanobubbles is shown by the model simulation of TDTR. A clear difference is seen in TDTR signal by the existence of only 1 nm gaseous phase. After confirming the existence of nanobubbles by AFM measurement, it can be proved that the nanobubbles are truly gaseous phase of the TDTR measurement.

Platinum hot-film sensors, whose typical size is 500nm wide × 10μm long × 40nm thick, are developed for investigating micro and nanoscale thermal events. This paper reports four kinds of applications with measurement principle, sensitivity analysis, and test results. Thermal conductivity of individual nanowire, represented by carbon nanotube, has been measured by bridging the specimen between the sensor and a heat sink. Here a new device is newly developed, which enables us to measure quantitatively both intrinsic thermal conductivity of the specimen and thermal contact resistance between the specimen and a target material. Focused beam-induced deposition is also measured by comparing the thermal conductance of deposited sensor and pristine one. Flow sensor is another application and we investigate the performance of carbon nanotube (CNT) fins deposited on the sensor by using dielectrophoresis technique to enhance the flow signal. The applicability of this sensor for measuring the thermal conductivity of fluid of very limited volume (femto-liter order) is also analytically studied.

We report on measurements of the growth rate of single budding yeasts with two microfluidic devices. One device is a MOSFET-based microfluidic Coulter-type sensor, which amplifies nonlinearly the resistance modulation from the translocation of budding yeast through the sensing microchannel. By moving a budding yeast cell back and forth through the sensing channel and measuring the induced resistance pulse from the translocation of the budding yeast, the volume growth rate of a budding yeast cell can be measured over its whole cell cycle. The other microfluidic device is based on comparing the resistance of the sensing microchannel with that of a reference microchannel, which eliminates the signal drift from the electrical conductivity change of the culture media. The reference channel-based sensing scheme enables real-time measurements of the volume growth rate of a budding yeast cell sitting in the sensing microchannel over a whole cell cycle. Measurement results from both devices show that the volume growth of single budding yeast is of sigmoid shape with a slow growth rate both before the bud emergence and at the end of the cell cycle. The device could be used for other important applications such as sensing the response of kidney cells to their micro-environments.

In this paper, a microflow cytometer for particles/cells passive focusing, fluorescence detection, and sizing is demonstrated with a convergent geometry of 50 μm detection gate channel and a pair of external optic fibers on poly-dimethylsiloxane (PDMS) microchip. A laser (635 nm) is used for fluorescent excitation. The amplitudes of the backward fluorescence signal and forward scattered light signal indicate the corresponding fluorescent intensity and size of the detected fluorescent particles and labeled white blood cells, respectively. In the experiment, the uniform fluorescent light intensity was measured by focusing the fluorescent particles in a 200×50×30μm detection gate channel. However, the emitted fluorescence and forward scattered light intensity of different size particles/cells are also measured simultaneously by external optic fibers.

AC electrothermal effect generates temperature gradients in the fluids, consequently inducing free charges that move in electric fields, and produce microflows in microchannel. This paper reports dramatic improvements in flow rate over conventional ac electrokinetic micropumps by exploiting asymmetry in electric potentials over the electrodes. A micropump consisting of planar asymmetric electrode array was tested using AC signals with and without a DC bias. The pumping velocity is much faster with a DC voltage, in some cases by an order of magnitude, reaching 3.2 mm/sec linear velocities with only 9 Vrms. Our hypothesis attributes the increase of ACET force to the ion generation near electrode by reactions and the resulting high conductivity gradient. The discovery presents an exciting opportunity for microfluidics, and further improvement can be anticipated with some optimization.

In this work, DEP platforms with funnelled and micro-tip electrode patterns were fabricated, and integrated with polydimethylsiloxane (PDMS) microchannel blocks. The DEP platforms were employed to manipulate polystyrene particles of 1 and 3 μm. The response of the system was characterised in a wide range of signal magnitudes (1–30 V peak-to-peak) and frequencies (100 kHz to 200 MHz), as well as the liquid flow rates (1 to 10 μL/min). Calculations were also carried out to analyse the DEP spectra of polystyrene particles when suspended in the medium (deionised water) to determine the optimum operating frequency of the DEP systems. Both experimental results and theoretical calculations indicated that polystyrene particles can experience positive and negative DEP forces within certain frequency ranges of the applied electric field, and the crossover frequency (where the DEP force is zero) of the system strongly depends on the conductivities of the particles. Additionally, larger particles experience stronger DEP forces and can be more efficiently concentrated at or repelled along the electrodes. The concentration performance of the DEP systems were evaluated by measuring the thickness of particle streams at different flow rates. Finally, the ability of funnelled and micro-tip electrodes to trap the particles was compared.

This paper reports on a thermal probe using a carbon nanotube (CNT) on a platinum hot-film. CNT probe is expected to breakthrough the limitations of the existing ones owing to its unique characteristics but no practical thermal device has been fabricated yet. In order to explore the mechanisms of heating and measuring the smaller region than 10nm, we applied our recently developed sensor coupled with CNT, which consists of a suspended platinum film of 40nm × 500nm × 10micrometer. The principle of this probe as heater and sensor is explained, based on one dimensional heat conduction. Fabrication process using MEMS technique is also introduced, especially for a couple of critical techniques. One is to fabricate the nano sensor on an edge of the sensor substrate. The other is to bond a CNT on the suspended hot-film sensor. A CNT thermal probe using a multi-walled CNT of 70nm diameter and ca. 10 micrometers length is successfully fabricated. Its performances are tested in vacuum environment as to eliminate the presence of in-air conduction effect and water absorption effect around the contact point, which work for heat transport dominantly in atmospheric condition and degrade the spatial resolution. Our CNT probe showed a clear and reliable signal in vacuum and its sensitivity available for nanoscale thermal sensing and heating is confirmed.

Nanofluidics is the science and technology involving a fluid flowing in or around structures with a least one dimension in the nanoscale, which is defined as the range from 1 nm to 100 nm. In this paper, we present the fabrication and characterization of nanochannels in silicon and glass. Since the lateral dimension of the channels is limited by the wavelength of UV light used in photolithography, the channel width can only be fabricated in the micrometer scale. However, the depth of the channel can be controlled precisely by etch rate of reactive ion etching (RIE). Microchannels and access holes were etched with deep reactive ion etching (DRIE). Both nanonochannel and microchannel were sealed by a Pyrex glass wafer using anodic bonding. The fabricated nanochannels were characterized by capillary filling and evaporation experiments. Due to the small channel height and weak fluorescent signal, fluorescent techniques are not suitable for the characterization of the nanochannels. A long exposure time due to the limited amount of fluorescent molecules inhibit the measurement of transient and dynamic processes. However, as the channel height shorter than all visible wavelengths, the contrast in refractive indices of air and liquid allow clear visualization of nanochannels filled with liquids. Automatic image processing with MATLAB allows the evaluation of capillary filling in nanochannels. Interesting phenomena and discrepancies with conventional theories are presented.

With the development of the ultra-short laser technology, a new optical detection field based on the transient laser pulse signals will emerge in the future. Ultra-short laser pulses have been used in biological fields to obtain the optical properties of vivo tissues. There are many numerical models to simulate the propagation of short laser pulses in tissue medium. However, since most biological tissues show a high scattering and low absorption characteristics for near-infrared light, the most popular model is diffusion approximation method. Although with many limitations, its greatest advantage is higher computational efficiency. The propagation of short pulse laser in two dimension nonuniform medium is simulated based on the diffusion approximation model in present paper. The numerical method is validated by comparing the numerical results with the theoretical analysis results in semi-infinite uniform slab medium. Then diffusion approximation is used to simulate the transfer process of ultra-short pulses in two dimensional inhomogeneous medium. Finally, The influences of inclusions with different sizes and optical properties on time-resolved reflected signals are presented. This can help to choose suitable detection parameters in diffuse optical tomography.

In a steam-compression refrigeration cycle, optimum heat exchange efficiency is acquired and compressor liquid hammer can be avoided if “zero superheat” arises at dry-evaporator outlet. Therefore zero superheat control study is of value. since refrigeration cycle will not get stable while it tends to hunt nearby zero superheat, expansion valve-dry evaporator regulation loop have to run at a positive superheat; and no fit theory is able to guide the design on the stability of expansion valve-dry evaporator regulation loop until the cause of refrigeration cycle hunting is found. Flow display experiments reveal the mechanism that refrigeration cycle will hunt next to 0 superheat while vapor/liquid two phase flow alternates at expansion valve exit. on the ground that phases can be told apart by thermal sensing rather than superheat, a specialized sensor has been developed to detect 0 superheat signal which serves as the feedback signal of expansion valve-dry evaporator regulation loop, the experiment results prove that the thermal sensor can afford 0 superheat.

Scanning Thermal Microscope (SThM) is known as a tool of the highest spatial resolution in measuring local temperature and thermophysical properties. However, despite the highest spatial resolution of SThM, its usefulness has been limited because of the difficulties related to the quantitative interpretation of the measured data. We suggest a double scan technique that can make an advantage of heat transfer through the tip-sample contact by subtraction of air conduction signal obtained from ‘lift mode’ scan. The thermal signal obtained by the new method is free from the influence of air conduction. This, in turn, allowed the quantitative profiling of the sample temperature.

DNA computation has shown its potential not only on mathematics, but on various practical areas such as diagnosis, single nucleotide polymorphism (SNP) detection, smart amplification, encryption and drug delivery etc. However, most previous researches about DNA computation possess a couple of weaknesses, including time-wasting, effort-wasting, lack of reusability and no miniaturization. In order to address this issue and improve weaknesses mentioned above, we built up a surface plasmon resonance (SPR) system for the detection on the DNA array chip to solve a 3-clause satisfiability (SAT) problem with 3 variables x, y and z. Every variable is defined as a 15-nt single strand DNA (ssDNA) which is immobilized on one spot of the gold surface. We further define SPR reflective intensity changes 0, 0.2 and 2 A.U. caused by changes of molecular weight on surface as Boolean signals False, True and None, respectively. Moreover, False signal represents a positive hybridization reaction via the hydrogen bond that binds the complementary ssDNA conjugating to IgG (150 kDa) by the crosslinker Sulfo-SMPB which can links thiol group labeled on ssDNA and amine group existed on IgG; True signal represents the hybridization reaction that binds the complementary ssDNA-IgG-Antigen which can result in a much larger intensity change. For a SAT problem F = (X T ∪ Y F )∩(X F ∪ Z T )∩(Y T ∪ Z T ), there are 8 possible answers. Therefore, we established a 3-spot array as a set which is immobilized sequence x, y and z. After one calculation, we read out the solution of this set and then regenerate it by injecting 0.05 N sodium hydroxide solution. In this work, we used 200 ng/ml X c -Human IgG, Y c -Rabbit IgG and Z c -Goat IgG as reaction agents for hybridization which represent False signal. Furthermore, 100 ng/ml Anti-Human IgG, Rabbit IgG and Goat IgG were taken as True signal agents. A full reaction can be completed within 30 minutes at room temperature. The buffer in the study is 1 x phosphate buffered solution (PBS) with 100 mM sodium chloride. The proposed platform has improved drawbacks that occurred in previous researches about DNA computer. Besides, it is provided with abilities a processor should have which are recalculable and realtime measurement so that provides us a novel approach for addressable and reusable diagnosis.

In this work, we found experimentally that there exist fairly strong fluid flows in AC electrowetting, which can be utilized as a means to mix the fluids in EWOD-based micro-devices. We visualized the internal flow. There may exist two distinct flow-generation mechanisms; one is the droplet oscillation, and the other is the electrohydrodynamic flow. The flow pattern is significantly dependent on the applied AC frequency. At low frequencies (represented here by 1 kHz), the center of the vortices is located somewhat randomly and the flow directs upward near the symmetric axis. At high frequencies (represented by 128 kHz), however, a pair of vortices having quite a regular structure is clearly visible and the flow directs downward near the symmetric axis. The flow patterns are strongly dependent on the position of the point electrode. The droplet surface undergoes a periodic oscillation (visualized by a high-speed camera) with a frequency exactly twice the frequency of applied electrical signal. The oscillating interface can generate a steady streaming. However the numerical results show that there exists no electric field at low AC frequencies. On the contrary, there exists quite a strong electric field inside the droplet at high frequencies. It means the electrohydrodynamic flow cannot be generated at the low frequency region, and the droplet oscillation might cause the flow generation at low frequencies. We also demonstrated the flow can be beneficially utilized as a mixing method.

The aim of this paper is to present a non-intrusive and optical method based on the classical thermal radiation laws for the measurement of microscale surface temperature. To overcome the diffraction limit, measurements are performed in the ultraviolet-visible range. According to the Planck’s law, emitting energy is low at these wavelengths and only a photonic flux can be measured through a cooled Photo-Multiplier Tube (PMT) and a photon-counting card. The photonic flux exhibits a random phenomenon that can be well-described through classical statistic laws such as Poisson or Normal distributions. We show in this paper that the signal we measure agrees well with these laws and that the surface temperature can be obtained either from the average or the standard-deviation of the Photonic flux. Multi-spectral techniques based on either physical and optical techniques like monochromatic filters and reflection/transmission diffraction gratings or digital techniques as a Multi-Channel Analyser (MCA) are proposed to get ride of the knowledge of the local surface emissivity. This is of a particular interest for the measurement of temperature in microscale applications. Finally, temperature measurements carried out on a specific High Temperature Blackbody developed in our laboratory are compared with those obtained through an infrared camera and allow to validate our facility and the presented measurement techniques.

Apertureless scattering near-field optical microscopy (A-SNOM) is generally performed using a heterodyne detection technique since it provides a higher signal-to-noise (S/N) ratio than homodyne detection. Accordingly, this study constructs a robust interference-based model of the detection signal which takes account of both the tip enhancement phenomena and the tip reflective background electric field to analyze the amplitude and phase of heterodyne detection signals at different harmonics of the tip vibration frequency. The analytical results indicate that the high-order harmonic tip scattering noise decays more rapidly with a high-order Bessel function for small phase modulation depths than the near-field interaction signal. It is also shown that the signal contrast improves as the wavelength of the illuminating light source is increased or the incident angle is reduced. As compared with homodyne technique, it can be found the signal contrast is much improved in visible region in heterodyne technique. The results presented in this study provide an improved understanding of the complex signal detected in the heterodyne A-SNOM technique and suggest potential means of improving its S/N ratio such that the signal contrast of heterodyne A-SNOM can be improved.