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Young Scientist Special Issue for 2019 MINE Young Scientist Award

The mission of the Young Scientists Forum is to promote Microsystems & Nanoengineering, the first engineering journal initiated by Nature Publishing Group in 2014. This forum provides scientists in the field of Microsystem & Nanoengineering from universities and research institutions worldwide an opportunity to present their latest research results. The Young Scientists Forum is organized by the editorial office of Microsystems & Nanoengineering, the State Key Laboratory of Transducer Technology (Chinese Academy of Sciences) and CINN. The "Young Scientists Awards" are selected by the organizing committee of the conference.

Part 1

Researchers in China have first time exploited the natural phenomenon of synchronization into practical sensor design, which significantly enhanced the resolution of microelectromechanical systems (MEMS) accelerometers. A team led by X.W. and Z.J. at Xi’an Jiaotong University achieved synchronization of the sensing oscillator in the accelerometer and an external reading oscillator through the injection locking. The synchronization leads to a fivefold boost in the resolution of the accelerometer. The team also developed a frequency-tracking system to break through the limitation of the synchronization range thereby enabling the device to work in a wider dynamic range. In addition to the direct application in accelerometers, the technique can also be used to improve the performance of other MEMS resonant sensors.

Article | Open Access | | Microsystems & Nanoengineering

A smart insole capable of monitoring a person’s gait could see use in wearable medicine, injury detection, or help to restore a healthy posture. Smart technologies capable of measuring physiological signals can help to monitor and improve human health. Recently, devices capable of mapping plantar pressure and distribution are seeing increasing use as predictors of a variety of health-related issues, such as exhausted running or walking, risk of slipping, or for detecting senile dementia. Led by Rongrong Bao from the Chinese Academy of Sciences, a team of researchers has developed an insole that uses an array of capacitive pressure sensors to monitor real-time data from static postures, such as standing or yoga poses, or dynamic activities like walking. The insole could see use as a wearable biosensor, in sports injury detection, or for diagnosing diseases.

Article | Open Access | | Microsystems & Nanoengineering

A fully integrated soft tactile sensor array (ISTSA) that is self-powered and without metal electrodes has been developed using a low-cost, easily performed fabrication process. A sensor array is a group of sensors used for collecting and processing electromagnetic signals, and arrays of tactile sensors have recently attracted substantial attention with the growth of wearable electronics and application in health monitoring and human-machine interfaces. A team headed by Yunlong Zi at The Chinese University of Hong Kong succeeded in developing an ISTSA with remarkable sensitivity. The ISTSA is so flexible that it exhibits excellent pressure sensing even in a curved state. The authors conducted real-time tactile sensing with LED lighting and finger touching, and they believe their ISTSA has considerable potential for application in such areas as position tracking, self-powered touch screens, and wearable electronics.

Article | Open Access | | Microsystems & Nanoengineering

The triboelectric effect is a type of contact electrification, and a liquid lens with variable focus has been developed using a triboelectric nanogenerator (TENG) where the focal length can be directly controlled by external mechanical sliding. With most artificial optical systems, adjusting the focal length is achieved by varying the spacing between the lenses, which results in complex mechanical designs and demands considerable space. However, a team headed by Chi Zhang at the Chinese Academy of Sciences, Beijing succeeded in producing a TENG-based varifocal liquid lens (TVLL), in which the TENG is used to accurately control the focal length of the lens by means of an external mechanical stimulus. The authors believe that their TVLL has excellent potential for application in such areas as micro-optical electromechanical systems, human-machine interactions, and artificial vision systems.

Article | Open Access | | Microsystems & Nanoengineering

Researchers have used techniques from origami to engineer a flexible, resilient, water-proof power generator, which can be used with wearable devices. The device, designed by a team led by Kai Tao of China’s Northwestern Polytechnical University, consists of two thin films of dielectric material, which can generate power when deformed. This structure is then folded in a Miura fold, a pattern which compresses a large surface area into a smaller area. The resulting spring-like makes the device return to its original shape after deformation while also offering compactness and flexibility together. The device generated power when tapped or bent, and the origami structure hermetically sealed the components, making the generator water-proof. With this combination of origami and material science, researchers can design and build flexible energy-harvesting devices to power wearable devices or other flexible electronics.

Article | Open Access | | Microsystems & Nanoengineering

A wearable thermoelectric device enables energy generation and sensing for health monitoring. Flexible electronic devices are promising candidates for personal health monitoring, and the ideal device would combine multiple functions in a single device. Two of the most important of these functions are energy generation and sensing. In this paper a team from University of Electronic Science and Technology of China led by Xiao-Sheng Zhang reports a thermoelectric-based device that combines these functions. Based on screen printing technology, they prepare n-type and p-type inorganic films onto a flexible polymer substrate, with their device being able to generate a voltage of up to 151 mV driven by a thermoelectric effect. The water sensitivity and temperature sensitivity of silk fibroin contained in the device enables moisture and temperature to be sensed.

Article | Open Access | | Microsystems & Nanoengineering

Researchers in China have developed a new type of radio frequency filter with extremely bandwidth widening capabilities, which will be useful for 5G networks. The approach is a hybrid configuration combining a microelectromechanical system (MEMS) filters combined with lumped elements. Dr. Tao Wu’s team at ShanghaiTech University began by modeling MEMS filters based on aluminum nitride resonators. They found that the first-order filter of proposed topology was several times better than existing systems at bandwidth, and that second-order filters improved rejection even further. Next, they fabricated a filter based on this design and characterized it. The bandwidth was approximately 12 times better than conventional standalone resonators. These designs will be valuable to filter out unwanted signals in 5G communications technologies.

Article | Open Access | | Microsystems & Nanoengineering

Part 2

A reusable, cost-effective, and environment-friendly PnP device has been developed for high-sensitivity immunoassays (biochemical tests that measure proteins or other substances through their properties as antigens or antibodies). Immunoassays are widely used in the diagnosis, screening, and monitoring of diseases. However, such techniques as enzyme-linked immunosorbent assay (ELISA), which are extensively applied in developed countries, are not widely available in developing nations owing to limited funding and lack of skilled manpower. They are also time consuming and lacking in sensitivity. A team headed by XiuJun Li at the University of Texas at El Paso produced a low-cost device using poly(methyl methacrylate) (PMMA or Perspex) that is 10 times more sensitive than commercial ELISA kits. The authors believe that their PMMA device offers considerable potential for application in detecting infectious diseases and cancers in resource-poor settings.

Article | Open Access | | Microsystems & Nanoengineering

A Lego-inspired, modular magnetic digital microfluidic architecture enables customizable bioanalysis. Magnetic digital microfluidics controls droplets on a surface via magnetic particles, with the liquid droplets themselves acting as mini bioreactors for analysis. Such devices often include surface energy traps to aide droplet manipulation. However, because they are fabricated as monolithic systems, they cannot be altered for different bioanalysis post-fabrication. Here, a team led by Yi Zhang from Nanyang Technological University, Singapore, reports a modular design for magnetic digital microfluidic devices, in which functional modules are configured and reconfigured via Lego-like studs. This modular design allows users to build testing platform on demand for a wide range of bioanalyses.

Article | Open Access | | Microsystems & Nanoengineering

A flexible, sensitive, stable neural probe consisting of boron-doped polycrystalline diamond (BDD) microelectrodes has been developed, whereby the BDD growth surface is used as the electrode site for neurophysiological and neurochemical sensing. Among carbon materials, BDD has found widespread use in neurotransmitter detection, but the hardness of diamond has impeded application in neural implants. A team headed by Wen Li at Michigan State University, USA, succeeded in developing a process that allows the growth side of the BDD thin film to be used as the sensing surface: they transferred the BDD patterns from a solid silicon substrate onto a flexible polymer substrate. The authors validated their BDD microelectrode technology for neural recordings both in vitro and in vivo, and they believe it has excellent potential for research into various brain disorders, such as Parkinson’s disease.

Article | Open Access | | Microsystems & Nanoengineering

A microcone is a microscopic cone, and a system based on a microcone array (MA) has been successfully developed and found to be effective as a neural interface. Implantable neural interfaces have received great attention through their broad applications in treating various neuropsychiatric disorders. However, acute inflammatory responses have hampered efforts to design a long-term, reliable implantable interface. A team headed by Xuemin Du and Yi Lu at the Chinese Aecademy of Sciences, Shenzhen, China succeeded in producing an MA-based living interface, which significantly elevated the activity of neurons and alleviated the inflammatory response at the interfaces after 6 weeks’ implantation in mouse brains. The authors believe that the excellent neuron network formation of their system offers considerable potential as a platform technology for developing next-generation artificial neural networks and brain-machine interfaces and for use in biomedical therapeutics.

Article | Open Access | | Microsystems & Nanoengineering

A novel probe combines electrochemical sensing and optical control in a single wireless device, enabling researchers to remotely influence animal behavior and simultaneously measure their dopamine response. In optogenetic systems, light is used to switch on specific genetically-engineered neurons. A team led by Xing Sheng of China’s Tsinghua University engineered a device with a microscale LED for optogenetic stimulation and an electrochemical sensor to detect dopamine. The two elements are separated by a diamond film for electrical and thermal insulation. The resulting device is roughly 2.2 × 1.3 cm and weighs 2 grams, including a miniaturized wireless circuit for control and a rechargeable battery for power. The team used the device to remotely train mice to prefer one chamber of a test environment via optogenetic stimulation and to measure animals’ dopamine response.

Article | Open Access | | Microsystems & Nanoengineering

Researchers in China have developed a new system to measure the concentration of ions in water to ensure that it is safe to drink. While ions can be easily detected with simple color-strip tests, quantitative measurement currently requires ion chromatography in a lab. Honglong Chang’s team at Northwestern Polytechnical University designed a device which uses chip-based ion chromatography using five electrodes to improve the signal-to-noise ratio. The team tested their device by using it to measure the concentration of several anions in tap water and found that it performed comparably to existing commercial ion chromatography systems.

Article | Open Access | | Microsystems & Nanoengineering

Taking inspiration from G-protein-linked receptors in biological cells, an artificial synapse is created for neuromorphic computing. Memristors are promising device units for the construction of neuromorphic computing platforms. Here, a team led by Ting Zhang from the Suzhou Institute of Nano-Tech and Nano-Bionics take inspiration from nature to fabricate a double-layer memristor. Specifically, they create a device that replicates the transmission of neural signals by ligands within G-protein-linked receptors. Their device includes a chitosan top-layer and a reduced graphene oxide bottom layer, with protons acting as charge carriers. Their device emulates some of the basic function of a synapse, including short-and long-term potentiation, spike-rate-dependent plasticity and learning/forgetting behavior.

Article | Open Access | | Microsystems & Nanoengineering

Part 3

Applying an electric field to individually trapped cells allows for the efficient and safe delivery of drugs or genes, and the characterization and manipulation of cellular activity. Electroporation is a technique that increases the permeability of a cell’s membrane, to allow the infiltration of drugs or genes. In practice, traditional electroporation has issues with efficiency and cellular damage. The scientists of Lingqian Chang (Beihang University) and Mo Li (Peking University Third Hospital) led a team to develop an on-chip “3D” system that uses a vacuum to trap cells in individual micropores. By applying an electric field, the team were able to deliver cargo of different sizes, from drugs to genes, into the cells with greater efficiency and safety than benchmark methods. The dose of chemotherapy drugs was controlled through altering the voltage applied. The team were able to inhibit tumor activity by delivering CRISPR-Cas9 gene editing plasmid with their system. This “3D” system was showed the potential for on-chip manipulation, in situ intracellular interrogation and cancer therapy.

Article | Open Access | | Microsystems & Nanoengineering

Calcium plays a critical role in the clustering of synaptic vesicles (which in a neuron store various neurotransmitters released at the synapse) induced by the protein alpha-synuclein, and different calcium concentrations exert different effects on such clustering. Alpha-synuclein is a key element in the development of Parkinson’s disease and other neurodegenerative conditions: it has been shown to interact with synaptic vesicles under the influence of calcium, but its physiological functions are poorly understood. Jiajie Diao of the University of Cincinnati College of Medicine, USA and colleagues used single-vesicle imaging to examine how calcium regulates vesicle clustering mediated by alpha-synuclein. They found that high calcium concentrations promoted vesicle clustering independent of alpha-synuclein, but low calcium concentrations inhibited vesicle clustering in an alpha-synuclein–dependent manner. The authors believe their findings provide insights into alpha-synuclein’s physiological function.

Article | Open Access | | Microsystems & Nanoengineering

Chinese scientists have developed a tunable membrane that is highly stretchable and could be used in a range of applications, including microfluidic devices, multiphase microreactors, and for particulate material synthesis. The ability to dynamically tune the transport behavior of gases and liquids is critical for membrane applications. And although recent tunable elastomeric membrane designs offer flexibility and anti-fracture properties, they have low tensile strength, are unreliable, and suffer from fouling. Now, Xu Hou and colleagues from Xiamen University in China use a novel liquid gating technology to develop a membrane made from graphene oxide-reinforced thermoplastic polyurethane that can be dynamically tuned for a wide range of gases and liquids, while also exhibiting anti-fouling properties. Liquid gating technology which uses a capillary-stabilized functional liquid to form reversible gates inside the pores, shows prominent properties in controlling complex, selective, multiphase substance transport. The liquid gating membrane is adaptable to different length scales, pressures, and environments and could be used in multiphase separation, chemical reactions, and drug delivery.

Article | Open Access | | Microsystems & Nanoengineering

A hybrid nanostructure can simultaneously repel contaminants and possess ammonia-sensing capabilities, making it an ideal pollution monitor. Gaseous pollutants such as ammonia have significant medical and environmental impacts. Hybrid structures of metal oxides and graphene have shown promising gas-sensing performance; however, their utility is hampered by the complexity of air composition and the presence of other contaminants. Xi Xie, of Sun Yat-Sen University, China, led a team of researchers to create a nanostructure of zinc oxide and graphene — both known as ammonia gas-sensitive materials — that repels liquids from its surface. The structure works by trapping “nano-air pockets” on the face of the device that prevent liquids from adhering to it, while the presence or absence of ammonia changes the conductivity of the nanostructure. The researchers’ paper shows an effective sensor for use in complicated environments.

Article | Open Access | | Microsystems & Nanoengineering

A solid lift-off method with an ingeniously designed micropore array as a shadow mask enables the efficient and precise control of cell patterning. Cell patterning is an important strategy for both basic biological mechanism studies and applicable technology developments in regenerative medicine, such as tissue engineering. Here, a team led by Prof. Wei Wang from Peking University presents the first report of a simultaneous control of cell alignment and adhesion/spreading via an easy single-step lift-off operation. The key concept is that the micropore array contains the large pores in central areas and small pores in surrounding areas controlling cell capture and alignment, and cell adhesion and spreading, respectively. They demonstrated high-throughput, high-efficiency cell alignment along with a precise control of cell spreading.

Article | Open Access | | Microsystems & Nanoengineering

Through using oil as a transient medium, a technique has been developed that can generate aqueous two-phase system (ATPS) droplets, thereby enhancing their application in various biological tests. Thanks to its ability to confine individual targets in microscale volumes, droplet microfluidics has great promise in processing and analyzing biological samples. Unfortunately, the ultra-low tension at the interface of ATPS (typically an aqueous solution of two incompatible polymers or one polymer and one salt) droplets has hampered their development for such applications despite their superiority over conventional water-in-oil droplets. However, a team headed by Ho Cheung (Anderson) Shum at the University of Hong Kong devised a simple strategy for using oil as a transient medium, which achieves a high throughput. The authors believe that their generation and sorting of ATPS droplets holds considerable potential for sophisticated microfluidic processing.

Article | Open Access | | Microsystems & Nanoengineering

Energy storage: Developing electrodes for potassium-based batteries. Microcubes of iron sulfide pyrrhotite constitute a promising electrode material for potassium-ion batteries. Potassium-ion (K+) batteries are being investigated as an alternative to lithium-ion batteries due to potassium’s abundance and low cost, but a challenge lies in discovering suitable materials for the battery’s electrodes. Yang Xu, and a team from University College London, United Kingdom, and Northeast Normal University, China, fabricated microcubes of pyrrhotite to use in K+ battery anodes to store ions. The anodes constructed by the team demonstrated a high capacity, with fast charge/discharge characteristics and stability that withstood repeated K+ insertion/extraction. Employing metal sulfides has cost and sustainability benefits, and the authors hope that their study can fuel further studies to realize the potential of K+ energy storage.

Article | Open Access | | Microsystems & Nanoengineering