Longwen Fu

Portable paper-based device for quantitative colorimetric assays relying on light reflectance principle

This paper presents a novel paper‐based analytical device based on the colorimetric paper assays through its light reflectance. The device is portable, low cost (<20 dollars), and lightweight (only 176 g) that is available to assess the cost‐effectiveness and appropriateness of the original health care or on‐site detection information. Based on the light reflectance principle, the signal can be obtained directly, stably and user‐friendly in our device. We demonstrated the utility and broad applicability of this technique with measurements of different biological and pollution target samples (BSA, glucose, Fe, and nitrite). Moreover, the real samples of Fe (II) and nitrite in the local tap water were successfully analyzed, and compared with the standard UV absorption method, the quantitative results showed good performance, reproducibility, and reliability. This device could provide quantitative information very conveniently and show great potential to broad fields of resource‐limited analysis, medical diagnostics, and on‐site environmental detection.

Magnetic molecularly imprinted microsensor for selective recognition and transport of fluorescent phycocyanin in seawater

Phycocyanin with excellent fluorescence characteristics and important physiological significance is an effective indicator for cyanobacterial bloom assessment due to its close relationship with cyanobacterial biomass. Molecularly imprinted polymers (MIPs) have attracted great interest owing to their recognition specificity; micromotor-driven targeted transport capability holds considerable promise. Herein, we propose an attractive magnetic microsensor for selective recognition, enrichment and transport of label-free fluorescent phycocyanin by combining MIPs and catalytic micromotors. The MIP-based catalytic microsensor was fabricated using phycocyanin as the imprinting molecule, Ni (0.55%) as the magnetic navigation material, and Pt (24.55%) as the solid support/catalyst to facilitate free movement in solutions, as well as an additional magnetic field was employed for trajectory control. The autonomous self-propulsion microsensor vividly displayed their motion states, presenting two different trajectories. The movement velocity was calculated based on the body-deformation model, suggesting a linear positive correlation between the velocity and hydrogen peroxide concentration, with a high average speed of 163 μm s−1. In addition, highly efficient targeted identification and enrichment abilities were demonstrated based on the magnetically imprinted layer. More excitingly, no obvious interference was found from complicated matrices such as seawater samples, along with real-time visualization of phycocyanin loading and transport. The sensing strategy would not only provide potential applications for rapid microscale monitoring of algae blooms, but also enrich the research connotations of protein imprinting.

Controlling Capillary-Driven Fluid Transport in Paper-Based Microfluidic Devices Using a Movable Valve

This paper describes a novel strategy for fabricating the movable valve on paper-based microfluidic devices to manipulate capillary-driven fluids. The movable valve fabrication is first realized using hollow rivets as the holding center to control the paper channel in different layer movement that results in the channels connection or disconnection. The relatively simple valve fabrication procedure is robust, versatile, and compatible with microfluidic paper-based analytical devices (μPADs) with differing levels of complexity. It is remarkable that the movable valve can be convenient and free to control fluid without the timing setting, advantages that make it user-friendly for untrained users to carry out the complex multistep operations. For the performance of the movable valve to be verified, several different designs of μPADs were tested and obtained with satisfactory results. In addition, in the proof-of-concept enzyme-linked immunosorbent assay experiments, we demonstrate the use of these valves in μPADs for the successful analysis of samples of carcino-embryonic antigen, showing good sensitivity and reproducibility. We hope this technique will open new avenues for the fabrication of paper-based valves in an easily adoptable and widely available way on μPADs and provide potential point-of-care applications in the future.

Surface-enhanced Raman scattering on a zigzag microfluidic chip: towards high-sensitivity detection of As(III) ions

In this study, a microfluidic platform was combined with surface-enhanced Raman scattering (SERS) to implement the rapid quantitative detection of As(III) ions in a continuous flow. Silver nanoparticles (AgNPs) were used as the SERS enhancement substrate, and glutathione (GSH) with 4-mercaptopyridine (4-MPY) was conjugated on the surface of the AgNPs. When As(III) ions encountered GSH/4-MPY functionalized AgNPs, the original monodispersed probes would aggregate because As(III) ions had a strong affinity to the GSH. As a result, Raman signals of 4-MPY adsorbed on the surface of the AgNPs were improved and the As(III) ions could be detected. Due to the advantages of microfluidics technology combined with SERS detection, the highly sensitive and reproducible analysis of As(III) ions was realized in several minutes. The proposed method allowed the quantitative analysis of As(III) ions with a linear range (3 to 200 ppb), and the limit of detection (LOD) of the As(III) ions was determined to be 0.67 ppb. The real water sample was also analyzed to confirm the practicability of the method and the consumption of several microliters of the sample was found to be environmentally friendly. This method also showed great potential in applying SERS combined with a lab-on-a-chip technique in the area of environmental monitoring with a high sensitivity and in an environmentally friendly way.

Molecular Imprinting Based Hybrid Ratiometric Fluorescence Sensor for the Visual Determination of Bovine Hemoglobin

We describe a simple and effective strategy to construct a molecular imprinting ratiometric fluorescence sensor (MIR sensor) for the visual detection of bovine hemoglobin (BHb) used as a model protein. The sensor was prepared by simply mixing the solution of green and red CdTe quantum dots (QDs), which were embedded in core-shell structured molecularly imprinted polymers and silica nanoparticles, respectively. The resultant hybrid MIR sensor can selectively bind with BHb and thus quench the fluorescence of the green QDs, while the red QDs wrapped with silica are insensitive to BHb with the fluorescence intensity unchanged. As a result, a continuous obvious fluorescence color change from green to red can be observed by naked eyes, with the detection limit of 9.6 nM. Moreover, the MIR sensor was successfully applied to determine BHb in bovine urine samples with satisfactory recoveries at three spiking levels ranging from 95.7 to 101.5%, indicating great potential application for detecting BHb in real samples. This strategy of using different fluorescence emission materials incorporated to construct a ratiometric fluorescence sensor is reasonable and convenient, which can be extended to the preparation of other ratiometric fluorescence systems for targeted analytes.

Simultaneous phase-inversion and imprinting based sensor for highly sensitive and selective detection of bisphenol A

A novel recognition element of molecularly imprinted films (MIFs) was synthesized by wet phase inversion (WPI) on the surface of Ti/TiO2 electrode for highly selective and sensitive electrochemical detection of bisphenol A (BPA). The Ti/TiO2/MIFs sensor was constructed by casting the precursor poly(acrylonitrile-co-acrylic acid) (p(AN-co-AA)) in dimethyl sulfoxide containing template molecule BPA onto the electrode and then immersing into water, resulting in simultaneous p(AN-co-AA) precipitation and BPA imprinting via the facile WPI. The imprinted sites could selectively rebind BPA through hydrogen bonding and hence lead to the equalizing current increase in amperometric detection, by which the BPA could be sensed electrochemically. Accordingly, the Ti/TiO2/MIFs sensor offered a favorable linearity within the wide range over five orders of magnitude (4.4nM-0.13mM), and a low detection limit down to 1.3nM. Excellent recognition selectivity for BPA was also attained over its analogues. Furthermore, this sensor was successfully applied to detect BPA in seawater and paper cup samples, and high recoveries were 86-110% with low relative standard deviations of 1.3-3.2%. By using BPA as a model, the MIFs-based method may provide a facile, rapid, and cost-effective way for ultrasensitive electrochemical measurements of various targeted compounds with good applicability to WPI.

Aquatic Toxic Analysis by Monitoring Fish Behavior Using Computer Vision: A Recent Progress

Video tracking based biological early warning system achieved a great progress with advanced computer vision and machine learning methods. Ability of video tracking of multiple biological organisms has been largely improved in recent years. Video based behavioral monitoring has become a common tool for acquiring quantified behavioral data for aquatic risk assessment. Investigation of behavioral responses under chemical and environmental stress has been boosted by rapidly developed machine learning and artificial intelligence. In this paper, we introduce the fundamental of video tracking and present the pioneer works in precise tracking of a group of individuals in 2D and 3D space. Technical and practical issues suffered in video tracking are explained. Subsequently, the toxic analysis based on fish behavioral data is summarized. Frequently used computational methods and machine learning are explained with their applications in aquatic toxicity detection and abnormal pattern analysis. Finally, advantages of recent developed deep learning approach in toxic prediction are presented.

Rotational Paper-Based Microfluidic-Chip Device for Multiplexed and Simultaneous Fluorescence Detection of Phenolic Pollutants Based on a Molecular-Imprinting Technique

In this study, we first present rotational paper-based microfluidic chips (RPADs) combined with a molecular-imprinting (MIP) technique to detect phenolic pollutants. The proposed rotational paper-based microfluidic chips could implement qualitative and quantitative analysis of two different phenolic contaminants, 4-nitrophenol (4-NP) and 2,4,6-trinitrophenol (TNP), simultaneously. Qualitative and quantitative analysis could be implemented simultaneously through fluorescence-intensity changes depending on the structures of quantum dots combined with a molecular-imprinting technique. Moreover, the rotational paper-based microfluidic chips provide a low cost, flexible, and easy way to operate the entire process conveniently. Under the optimal conditions, the proposed sensors showed high sensitivity and selectivity. Our final experimental results illustrated that the detection limits of 4-NP and TNP in the paper-based quantum-dot MIP (PQ-MIP) RPADs ranged from 0.5 to 20.0 mg/L, with detection limits of 0.097 and 0.071 mg/L, respectively. This novel rotational paper-based microfluidic device shows great potential and versatility for multiplexed, portable, and rapid testing of environmental and biological samples in the future.