A room temperature liquid metal-based microvalve has been proposed in this work. The microvalve has the advantages of easy fabrication, high flexibility, and a low leak rate. By designing a posts array in the channel, the liquid metal can be controlled to form a deformable valve boss and block the flow path. Besides, through adjustment of the pressure applied to the liquid metal, the microvalve can perform reliable switching commands. To eliminate the problem that liquid metal is easily oxidized, which causes the microvalve to have poor repeatability, a method of electrochemical cathodic protection has been proposed, which significantly increases the number of open/close switch cycles up to 145. In addition, this microvalve overcomes the shortcomings of the traditional microvalve that requires an alignment process to assemble all the parts. When the valve is closed, no leak rate is detected at ≤320 mbar, and the leak rate is ≤0.043 μL/min at 330 mbar, which indicates it has good tightness. As an application, we also fabricate a chip that can control bubble flow based on this microvalve. Therefore, this microvalve has great prospects in the field of microfluidics.

Here, we report a novel technology for the fabrication of copper-electroplating-modified liquid metal microelectrodes. This technology overcomes the complexity of the traditional fabrication of sidewall solid metal electrodes and successfully fabricates a pair of tiny stable solid-contact microelectrodes on both sidewalls of a microchannel. Meanwhile, this technology also addresses the instability of liquid metal electrodes when directly contacted with sample solutions. The fabrication of this microelectrode depends on controllable microelectroplating of copper onto the gallium electrode by designing a microelectrolyte cell in a microfluidic chip. Using this technology, we successfully fabricate various microelectrodes with different microspacings (from 10 μm to 40 μm), which were effectively used for capacitive sensing, including droplet detection and oil particle counting.

This work proposes a liquid–metal-based calorimetric micro-flow sensor within a polydimethylsiloxane (PDMS) chip. It can measure the flow rate of fluid in microscale channels, with a range as low as several microliters per minute. This in-chip sensor is proposed to solve the issue of detecting the flow rate in microfluidic systems. To make the sensor compatible with PDMS microfluidic chips, low-melting-point gallium-based alloy and bismuth-based (bi-based) alloy are used to make the micro heater and bi-metal thermocouples, for these alloys can be easily injected into a PDMS chip to form electrodes. To minimize heat resistance (or temperature difference) between fluid and the detecting ends of thermocouples, these ends are directly exposed to liquid in the flow channel with the help of a special reversible bonding technology. Thermocouples are connected in series to improve the sensor’s response. A novel method to bond and electrically connect the sensor to a print circuit board is also elaborated. Since the calorimetric flow sensor is sensitive to heating power, fluid temperature and environment cooling, a dimensionless parameter less independent of these factors is deduced from heat transfer theory, and this idea is used in result processing to offset the bad effect. Experiments with pure water show that this sensor can be used to detect flow rates, with a resolution up to 4 µl min⁻¹ mV⁻¹ and a range of 12 µl min⁻¹ in this case, and that at different heating powers, the thermal potential results vary significantly whereas the dimensionless results nearly keep the same. Present work indicates that this sensor has the potential to be integrated into a PDMS microfluidic system and to provide accurate and stable results if a dimensionless method is used in data processing.

Formaldehyde poses a critical indoor environmental health hazard, particularly in rapidly urbanizing settings. Residential and public buildings serve as the most significant exposure sites; however, the extent of urban populations’ formaldehyde exposure in these two types of environments remains unclear, posing challenges for precise prevention and control strategies. This study employed a comprehensive exposure assessment by combining personal exposure monitoring with environmental sampling to characterize formaldehyde exposure profiles and contributions apportioned to residential and public microenvironments. The mean personal exposure concentration of formaldehyde of working adults was 36.0 μg/m³ (SD: 30.7 μg/m³). The mean chronic daily intake derived from personal data was 5.1 μg/kg/day. Residential environments were identified as the predominant contributors to overall exposure (>50% of total exposure in working adults, and >80% in children/elderly), followed by public places (contributing to 40% among employed adults). For children under 5 years and the elderly, residential settings accounted for >80% of the contribution of total intake. The home and school environments contributed to approximately 60% and 30% of exposure for children and adolescents aged 5–18 years, respectively. Other microenvironments (such as vehicular and outdoor settings) contributed to less than 10%. Simulation scenarios further suggested that reducing indoor formaldehyde concentrations by 15–30% in both residential and public buildings could avert 10–20% of associated health burdens for targeted populations. These findings underscore the continuous need for formaldehyde exposure control in both residential and public environments as well as indoor health interventions in modern urban areas.

In this paper, we propose a novel liquid metal microheater utilizing a textured structure. This microheater effectively solves the problem of the liquid metal in the PDMS flow channel fracturing at a certain temperature and significantly increases the maximum operating temperature that can be achieved by the current liquid metal microheater. Experimental results demonstrate that this new structured microheater can achieve a maximum operating temperature exceeding 300 °C. To explain the performance improvement and the reasons behind liquid metal fracture, corresponding experiments were conducted, and explanations were provided based on the experimental results. Subsequently, we verified the mechanical flexibility of the microheater and found that it exhibits excellent tensile and bending resistance. Finally, utilizing its good mechanical flexibility, the microheater was successfully attached to the side wall of a cup, resulting in the boiling of water.