Xuming Zhang

The Hong Kong Polytechnic University | PolyU · Department of Applied Physics

Plasmon‐enhanced photocatalysis has emerged as a promising technology for solar‐to‐chemical energy conversion. Compared to isolated or disordered metal nanostructures, by controlling the morphology, composition, size, spacing, and dispersion of individual nanocomponents, plasmonic nanostructure arrays with coupling architectures yield strong broadb...

Ultrasensitive nanomechanical instruments, e.g., atomic force microscopy (AFM), can be used to perform delicate biomechanical measurements and reveal the complex mechanical environment of biological processes. However, these instruments are limited because of their size and complex feedback system. In this study, we demonstrate a miniature fiber op...

Microfluidic integration promotes multiplexing opportunities for the plasmonic biosensors in the simultaneous detection of multiple analytes. This chapter gives a detailed account of the recent advances and progress made by microfluidic-based plasmonic biosensors for applications in various biomedical detection fields. Particularly, different types...

Alpha-fetoprotein (AFP) is a serum biomarker mainly for early-stage diagnosis and prognosis of primary liver cancer in clinical analysis. As a label-free analyte-specific biosensor with ultrahigh sensitivity and broad detection range, photoelectrochemical (PEC) sensor is promising for AFP detection. A unique feature of the PEC sensor, the separatio...

There is a growing need to measure respiratory rate (RR) in a variety of applications, including in clinical and occupational settings, as well as during physical exercises. Fiber optic sensors (FOSs) is an attractive solution for wearable RR monitoring because of their small size, multiplexing capability, chemical inertness, and immunity to electr...

Carbon capture and utilization (CCU) of microorganisms is widely expected to provide fresh insight into oil wastewater treatment due to green and sustainable processing, and the constant pursuit of high efficiency and sufficient waste utilization to combat climate change calls for the development of advanced engineering microbiology. Here, we explo...

By geometrically constraining fluids into the sub-millimeter scale, microfluidics offers a physical environment largely different from the macroscopic world, as a result of the significantly enhanced surface effects. This environment is characterized by laminar flow and inertial particle behavior, short diffusion distance, and largely enhanced heat...

Four interrelated issues have been arising with the development of modern industry, namely environmental pollution, the energy crisis, the greenhouse effect and the global food crisis. Photocatalysis is one of the most promising methods to solve them in the future. To promote high photocatalytic reaction efficiency and utilize solar energy to its f...

D-π -A type 4-((9-phenylcarbazol-3-yl)ethynyl)-N-dodecyl-1,8-naphthalimide (CZNI) with a large dipole moment of 8.49 D and A-π-A type bis[(4,4’-1,8-naphthalimide)-N-dodecyl]ethyne (NINI) with a negligible dipole moment of 0.28 D, were smartly designed and synthesized to demonstrate the evidence of molecular dipole as the dominant mechanism for cont...

D-π -A type 4-((9-phenylcarbazol-3-yl)ethynyl)-N-dodecyl-1,8-naphthalimide (CZNI) with a large dipole moment of 8.49 D and A-π-A type bis[(4,4’-1,8-naphthalimide)-N-dodecyl]ethyne (NINI) with a negligible dipole moment of 0.28 D, were smartly designed and synthesized to demonstrate the evidence of molecular dipole as the dominant mechanism for cont...

Chloroplast of plants is a natural microfluidic reactor for natural photosynthesis, in which, the multi-enzymatic Calvin cycle is the key. In chloroplast, the Calvin cycle enzymes are reportedly attached to...

In this work, the Co-Ni basic carbonate nanowires were in-situ grown on carbon nanotube (CNT) network through a facile chemical bath deposition method, which could be further converted into active hydroxide via cyclic voltammetry strategy. A series of carbonate nanowire/nanotube with different Co/Ni ratio revealed the different growth status of the...

Solar water splitting by photoelectrochemical (PEC) reactions is promising for hydrogen production. The gold nanoparticles (AuNPs) are often applied to promote the visible response of wideband photocatalysts. However, in a typical TiO2/AuNPs structure, the opposite transfer direction of excited electrons between AuNPs and TiO2 under visible light a...

This review aims to summarize the recent advances and progress of plasmonic biosensors based on patterned plasmonic nanostructure arrays that are integrated with microfluidic chips for various biomedical detection applications. The plasmonic biosensors have made rapid progress in miniaturization sensors with greatly enhanced performance through the...

Plasmon-induced hot carriers have recently attracted intensive research, but the energy efficiency in the visible light is often low due to the short lifetime of hot carriers and the limited optical absorption of plasmonic architectures. To boost the generation of hot carriers, here we propose to exert multiple plasmonic resonant modes and their st...

Fig. S1. The SEM image (left) and the distribution of the diameter of holes (right) extracted from the SEM image. The average and standard deviation of the holes' diamter are 222 nm and 4.01 nm, respectively. Electronic Supplementary Material (ESI) for Nanoscale. This journal is

This work reports a Cu 2 O/AuNPs/NiO/FTO photocathode with the increased photocurrent density in visible light caused by the enhanced electromagnetic (EM) fields of Au nanoparticles (AuNPs) and efficient electron/hole separation by NiO hole transport layer (HTL). © 2021 The Author(s)

This paper successfully prepared a unique titanium dioxide nanorod arrays nanocomposite doped with carbon quantum dots and gold nanoparticles as a high‐efficiency photocatalyst. Due to their enhanced electron–hole separation efficiency and strong light‐scattering effects, one‐dimensional nanostructured titanium dioxide nanorods were utilised as the...

Two charged organic semiconductors based on naphthalimide bolaamphiphiles were designed to fabricate metal–insulator–semiconductor (MIS) photosystems with opposite‐charged DuBois nickel catalysts for biomimetic H2 evolution. The photoinduced charge carriers can be efficiently separated and tunneled to the Ni collectors across salt bridges and alkyl...

Polluted sea water is a common problem in coastal cities, but its decontamination remains a big challenge due to the existence of salt ions, which may invalidate many prevailing treatment methods originally developed for waste fresh water. This work presents the first attempt to decontaminate the polluted sea water by synergizing two separate proce...

This paper reports an electrically generated optical waveguide for the transverse-magnetic wave. The waveguide is formed in a z-cut single-crystal lithium-niobate (LN) thin film by the electro-optic effect, where the extraordinary refractive index (RI) of the LN film is increased by a voltage applied to patterned electrodes that define the waveguid...

This special issue is a collection of 12 technical papers and two reviews that are expanded into full-length articles from the conference abstracts of the 9th International Multidisciplinary Conference on Optofluidics (IMCO 2019) held in Hong Kong in 14–17 June 2019 [...]

Hydrogen as an antioxidant gas has been widely used in medical and biological fields for preventing cancer or for treating inflammation. However, controlling the hydrogen concentration is crucial for the practical use due to its explosive property when its volume concentration in air reaches the explosive limit (4%). In this work, a polymer based m...

A novel mechanism of sensitivity enhancement of D-shaped fiber-based surface plasmon resonance (SPR) sensors for the optofluidic device has been proposed. The sandwiched structure optofluidic platform is developed with metal-coated D-shaped fiber as the sensing device, while another thin metal layer is situated under the inner wall of the substrate...

A volume refractive index (RI) sensor based on the resonant optical tunneling effect (ROTE) is presented in this study. Compared with the classic volume RI sensing structure, the Fabry-Pérot (FP) etalon, the ROTE structure has a higher figure of merit (FOM) than that of the FP cavity with the same cavity length. The sensitivity of the ROTE structur...

This paper proposes and analyzes a parity-time (PT) symmetry structure based on resonant optical tunneling effect (ROTE) by using two directly coupled ROTE resonators to achieve a balanced gain-loss distribution. The unbroken/broken states of the PT symmetric system are theoretically verified by coupled-mode theory (CMT), transmission matrix method...

Aberration is a long-standing problem of fixed focal lenses and usually requires a complicated lens set to compensate. It becomes more challenging for tunable lenses. This paper reports an original design of in-plane optofluidic lens that enables to compensate the spherical aberration during the tuning of focal length. The key idea is to use two ar...

As an environment-friendly semiconductor, titanium dioxide (TiO2), which can effectively convert solar energy to chemical energy, is a crucial material in solar energy conversion research. However, it has several technical limitations for environment protection and energy industries, such as low photocatalytic efficiency and a narrow spectrum respo...

This work reports a microfluidic reactor that utilizes gold nanoparticles (AuNPs) for the highly efficient photocatalytic degradation of organic pollutants under visible light. The bottom of microchamber has a TiO2 film covering a layer of AuNPs (namely, TiO2/AuNP film) deposited on the F-doped SnO2 (FTO) substrate. The rough surface of FTO helps t...

A novel metal‐insulator‐semiconductor (MIS) photosystem based on covalent organic frameworks (COFs) semiconductors was designed smartly to allow for robust and efficient hydrogen evolution under visible light irradiation. A maximal H 2 evolution rate of 8.42 mmol h ‐1 •g ‐1 and an impressive turnover frequency of 789.5 h ‐1 were achieved in such an...

A unique type of refractive index (RI) sensor is proposed using a dual Mach-Zehnder interferometer (MZI) structure based on side-hole fibers (SHFs). The MZI structure contains two single-mode fibers (SMFs), two coreless fiber (CLF) sections and an SHF section, which are spliced together in the order of SMF-CLF-SHF-CLF-SMF. The SMFs and the CLFs ena...

Biocatalysis has attracted significant attention owing to their environmental-friendly nature, high efficiency and remarkable selectivity during reactions. However, enzymes, one powerful catalyst used in biocatalysis, suffer from low stability for long time operation in solution and gradual decrease of activity in storage. Microfluidic reactors are...

Food production in green crops is severely limited by low activity and poor specificity of D-ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in natural photosynthesis (NPS). This work presents a scientific solution to overcome this problem by immobilizing RuBisCO into a microfluidic reactor, which demonstrates a continuous production of g...

This paper presents an original design for a volume refractive index (RI) sensor for cell concentration detection based on the unique resonant optical tunneling effect (ROTE). In this design, the solution sample is introduced into the ROTE resonant cavity, whose reflection spectrum presents a large shift of its resonant dip in response to the tiny...

Metamaterial assisted terahertz (THz) label-free bio-sensing has promising applications. However, the sensitive THz detection of highly absorptive liquid samples remains challenging. Here, we present a novel multi-microfluidic-channel metamaterial biosensor (MMCMMB) for highly sensitive THz sensing of small volume liquid samples. The multi-channels...

Optical polarization imaging has played an important role in many biological and biomedical applications, as it provides a label-free and non-invasive detection scheme to reveal the polarization information of optical rotation, birefringence, and photoelasticity distribution inherent in biological samples. However, the imaging speeds of the previou...

Here we report a planar polarization rotator using a nematic liquid crystal waveguide, which is subject to a gradient electric field in parallel to the waveguide substrate plane. The fabricated polydimethylsiloxane (PDMS) device has demonstrated the electrically-controlled polarization rotation at a switching time of 70 ms and a propagation loss of...

This paper reports an electrically reconfigurable optofluidic lens with two air-liquid (silicone oil) interfaces actuated by the dielectrophoretic (DEP) force. Initially, a symmetric biconcave air-liquid lens is formed by the surface tension in a microfluidic chip. Then, the DEP force deforms the air-liquid interfaces from biconcave to biconvex, tu...

Electrochemical catalysts for the oxygen evolution reaction (OER) play a key role in highly-efficient water splitting and many other important energy conversion applications. Transition metal oxides are promising OER catalysts. In this work, Fe, W co-doped Co3O4 was grown on carbon fiber cloth (FeWCo3O4/CFC) and polypyrrole (PPy)/carbon fiber cloth...

Methylammonium lead iodide perovskite (MAPbI3), as a new type of light absorber for optoelectronic devices, has attracted much interest and served as foundation for new device concepts. However, most studies to date are mainly focusing on the fabrication of MAPbI3-based solar cells and photodetectors. Here we report a facile method to prepare a lar...

Plasmon‐induced hot carriers have vast potential for light‐triggered high‐efficiency carrier generation and extraction, which can overcome the optical band gap limit of conventional semiconductor‐based optoelectronic devices. Here, it is demonstrated that Au/TiO2 dumbbell nanostructures assembled on a thin Au film serve as an efficient optical abso...

Plasmonics sensitization enables semiconductors absorbing sub‐bandgap photons through the generation of hot carriers in metallic nanostructures and subsequent transfer to adjacent semiconductors. To that end, Dang Yuan Lei and co‐workers present a Au@TiO2 dumbbell‐on‐film nanocavity in article number 1800383. Non‐radiative decay of the localized su...

This paper proposes a compact planar optofluidic optical cross-connect (OXC) switch based on electro-optic (EO) waveguides in nematic liquid crystal (NLC). In the cross-bar fabric, each unit cell of the proposed device consists of two portions: the NLC EO waveguides for 1 $\times$ 2 switching and the fixed NLC-core waveguides to support subsequent...

Resonant optical tunneling effect (ROTE) is a special phenomenon that light can fully go through the seemingly impenetrable optical structure. It is a prominent example to study the analogy of wave optics and quantum physics. Previous theoretical work mostly focused on the optical modeling of transmission spectrum using the transfer matrix method (...

This paper reports a tunable in-plane optofluidic lens by continuously tuning a silicone oil-Air interface from concave to convex using the dielectrophoresis (DEP) force. Two parallel glasses are bonded firmly on two sides by NOA 81(Norland Optical Adhesive 81) spacers, forming an open microfluidic channel. An ITO (indium tin oxide) strip and anoth...

Optofluidics incorporates optics and microfluidics together to construct novel devices for microsystems, providing flexible reconfigurability and high compatibility. Among many novel devices, a prominent one is the in-plane optofluidic lens. It manipulates the light in the plane of the substrate, upon which the liquid sample is held. Benefiting fro...

This paper presents the device design and performance analysis of a novel design of planar optical cross-connect (OXC) using nematic liquid crystal (NLC) waveguides. It employs N × N switching matrix in cross-bar fabric. In each unit cell, the input light is set in either the transverse electric (TE) mode or the transverse magnetic (TM) mode by ele...

Artificial photosynthesis (APS) mimics natural photosynthesis (NPS) to store solar energy in chemical compounds for applications such as water splitting, CO2 fixation and coenzyme regeneration. NPS is naturally an optofluidic system since the cells (typical size 10 to 100 µm) of green plants, algae, and cyanobacteria enable light capture, biochemic...

The liquid cloak controlled by the diffusion is analogous to its counterpart designed by transformation optics. Avoiding the nanofabrication processing of previous invisible cloak, the liquid media form the refractive index profile by convection‐diffusion process. This work applies optofluidic technology and can realize the real‐time tunable of clo...

A method is introduced for the design of invisibility cloaks inspired by fluid dynamics that is different from traditional transformation optics. The inhomogeneous refractive index of the liquid cloak controlled by the natural liquid diffusion is analogous to its counterpart designed by transformation optics. Here, a tunable liquid visible cloak is...

Decontamination of seawater is of particular importance for the waste seawater treatment before its drainage. However, some mature methods to clean waste fresh water cannot be employed to treat waste seawater due to its high slat concentration. Besides, excessive chlorine generation during the seawater decontamination process is toxic for sea creat...

Although silicon has been widely employed as light harvesting antenna in photocatalysts due to its cost advantage , it suffers from low efficiency and poor stability due to photocorrosion of Si. To overcome this problem, a heterojunction photocathode was produced by coating a WS 2 thin-film on p-type Si. Our proposed method can further improve the...

Methods and mechanisms for improvement of photocatalytic activity, are important and popular research topics for renewable energy production and waste water treatment. Here, we demonstrate a facile laser drilling method for engineering well-aligned pore arrays on magnetron-sputtered WS2 nanofilms with increased active edge sites; the proposed metho...

Artificial photosynthesis is the imitation of natural photosynthesis, which promises an efficient way to use solar energy to synthesize organic matters, in which the key step is the coenzyme regeneration (NADH/NADPH). To achieve an efficient regeneration rate, various photocatalysts have been developed, such as g-C3N4 and mesoporous carbon nitride...

The issue of thermal effects is inevitable for the ultrahigh refractive index (RI) measurement. A biosensor with parallel-coupled dual-microring resonator configuration is proposed to achieve high resolution and free thermal effects measurement. Based on the coupled-resonator-induced transparency effect, the design and principle of the biosensor ar...

Acceleration is a significant parameter for monitoring the status of a given objects. This paper presents a novel linear acceleration sensor that functions via a unique physical mechanism, the resonant optical tunneling effect (ROTE). The accelerometer consists of a fixed frame, two elastic cantilevers, and a major cylindrical mass comprised of a r...

A plasmonic black absorber is developed by X. Zhang and co-workers in article number 1600399 by sandwiching a 150-nm TiO2 layer between a layer of random Au nanoparticles and a rough Au surface (200 nm thick). The combined plasmonic effect of the Au nanoparticles and the Au rough surface enables a strong absorption (72%–91%) over 400–900 nm and enh...

Precise sorting of gold nanoparticles is important but it still remains a big challenge. Traditional methods like centrifugation can separate nanoparticles with a high throughput but at the cost of low precision. Optical tweezers enable the precise manipulation of a single nanoparticle in steady liquid environments. However, this method may become...

Measuring the charge of a nanoparticle is of great importance in many fields including optics, astronomy, biochemistry, atmospheric science, environmental engineering, and dusty plasma. Here, we propose to use a high-Q whispering-gallery-mode (WGM) optical microresonator to detect the surface and bulk charge of a dielectric nanoparticle. Because of...

We propose herein, a one-step method to assemble the immobilized artificial photosystem I (IAPSI) in a microfluidic chip, which integrated a preformed graphitic carbon nitride photocatalyst (g-C3N4) and electron mediator (M) in one chip and mimicked the characteristics of photosystem I. The simultaneous assembly of g-C3N4 and M could efficiently re...