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“Lab on paper” is a paper-based microanalytical system with unique advantages such as high sensitivity, low cost, portability, and mass production, which breaks through the limitations of traditional detection technologies and shows great potential in the field of rapid on-site food detection. In this paper, the typical “labs on paper”, including chromatographic paper, chemical test chip, lateral flow assay (LFA), microfluidic paper-based analytical devices (μPADs), and synthetic biological paper, are systematically reviewed. Special emphasis is put on the application of “lab on paper” in the field of food detection. Finally, the advantages, challenges, and future prospects of paper-based analytic methods are discussed, which may provide theoretical support for better application of “lab on paper” in the field of food detection.

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Analytical applications of paper-based microfluidic devices, receive much attention and have been heavily investigated in the last few years. Liquid movement in the body of the paper brings the idea of paper-based flow injection analysis (FIA) developed according to lab-on-paper (LOP) concept. In this approach, paper patterned with hydrophobic borders playing the role of channels in FIA system. The channel is connected from one side with an unlimited source of the liquid carrier and from the other side with sorbent pad, which ensures constant and a continued flow of fluid along the channel. Microliter volumes of standards, consecutively placed directly on the paper surface are moving towards detection zone. The developed prototype of LOP-FIA system was tested with the dedicated optoelectronic detector, compatible with a model analyte (bromothymol blue) as well as with Prussian Blue based chemosensitive layer deposited inside a paper channel, playing the role of the prototype of the flow-through optical sensor integrated with LOP. The effects of sorbent/channel type, distance between injection and detection zone and sample volume on the shape of the analytical signal were investigated. Results obtained for sequential sample introduction show satisfactory reproducibility, confirming that paper-based microfluidic FIA without conventional tubing, pumps and valves, exploring merits of LOP concept only, is possible. [ABSTRACT FROM AUTHOR]

We describe herein the fabrication of an electrochemical microfluidic paper based device (EμPAD) for the detection of diazepam, a sedative, anxiety-relieving and muscle-relaxing drug. To achieve it, silica coated gold nanorods (Si@GNRs) were synthesized and drop casted on an electrochemical microfluidic paper based device (EμPAD) for the detection of diazepam. The synthesized composites were characterized by recording its images in scanning electron microscope (SEM) and transmission electron microscope (TEM). The experimental results confirmed that Si@GNRs had good electrocatalytic activity towards diazepam. The modified paper based electrode showed a stable electrochemical response for diazepam in the concentration range of 3.5 nM to 3.5 mM. EμPAD offers many advantageous features such as facile approach, economical and have potential for commercialization. Si@GNRs modified EμPAD was also employed for determination of diazepam in spiked human urine samples. Reported facile lab paper approach integrated with Si@GNRs could be well applied for the determination of serum metabolites. [ABSTRACT FROM AUTHOR]

We describe a paper-based chemiluminescence (CL) test for the determination of mercury(II) ion. A single-stranded DNA aptamer was first covalently immobilized via its amino groups to the hydroxy groups on the surface of cellulosic paper. The aptamer probes can capture Hg(II) ions due to their specific interaction with thymine. The CL reagent (a caboxylated phenylene-ethynylene referred to as P-acid) was immobilized on nanoporous silver (NPS@P-acid) and used a CL label on the aptamer. The stripe is then contacted with a sample containing Hg(II) ions and CL is induced by the addition of permanganate. CL intensity depends on the concentration of Hg(II) because Hg(II) increases the quantity of the P-acid-conjugated aptamer. The highly active surface of the NPS@P-acid composites results in an 8-fold higher CL intensity compared to the use of pure P-acid. This enables Hg(II) ion to be quantified in the 20 nM to 0.5 μM concentration range, with a limit of detection as low as 1 pM. This CL aptasensor is deemed to represent a promising tool for simple, rapid, and sensitive detection of Hg(II). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The detection of pesticides has attracted considerable attention in numerous fields, such as environmental monitoring and food safety. Although traditional sensors for pesticides have been widely explored due to their high sensitivity and specificity, it is still challenging to develop a low-cost, portable, fast, and easy-to-use detection method for the public use at home or in the field. To address these challenges, herein, we report a novel paper-based molecular imprinted polymer (MIP)-grafted multi-disk micro-disk plate (P-MIP-MMP) for sensitive and specific chemiluminescence (CL) detection of pesticides through an indirect competitive assay using 2,4-dichlorophenoxyacetic acid (2,4-D) as a proof-of-concept analyte. The MIP-grafted paper disks were prepared by a simple in situ polymerization of MIP layer on the surface of cellulose fibers in paper. The quantification mechanism of this P-MIP-MMP is based on a competition between free 2,4-D and tobacco peroxidase (TOP) labeled 2,4-D and the enzyme catalyzed CL emission from the luminol-TOP-H2O2 CL system. At optimal conditions, this P-MIP-MMP can detect 2,4-D at the concentration of femtomolar level. This approach provided a powerful protocol for simple, low-cost, rapid, and high-throughput detection of pesticides in real samples with satisfactory results for use in areas such as food inspection and environmental monitoring. [Copyright &y& Elsevier]

Abstract: In this study, electrochemical immunoassay was introduced into the recently proposed microfluidic paper-based analytical device (μPADs). To improve the performance of electrochemical immunoassay on μPAD for point-of-care testing (POCT), a novel wax-patterned microfluidic paper-based three-dimensional electrochemical device (3D-μPED) was demonstrated based on the multi-walled carbon nanotubes (MWCNTs) modified μPAD. Using typical HRP-O-Phenylenediamine-H2O2 electrochemical system, a sandwich immunoassay on this 3D-μPED for sensitive diagnosis of two tumor markers simultaneously in real clinical serum samples was developed with a linear range of 0.001–75.0UmL−1 for cancer antigen 125 and 0.05–50.0ngmL−1 for carcinoembryonic antigen. In addition, this 3D-μPED can be easily integrated and combined with the recently emerging paper electronics to further develop simple, sensitive, low-cost, disposable and portable μPAD for POCT, public health and environmental monitoring in remote regions, developing or developed countries. [Copyright &y& Elsevier]

Abstract: In this work, electrochemiluminescence (ECL) immunoassay was introduced into the recently proposed microfluidic paper-based analytical device (μPADs) based on directly screen-printed electrodes on paper for the very first time. The screen-printed paper-electrodes will be more important for further development of this paper-based ECL device in simple, low-cost and disposable application than commercialized ones. To further perform high-performance, high-throughput, simple and inexpensive ECL immunoassay on μPAD for point-of-care testing, a wax-patterned three-dimensional (3D) paper-based ECL device was demonstrated for the very first time. In this 3D paper-based ECL device, eight carbon working electrodes including their conductive pads were screen-printed on a piece of square paper and shared the same Ag/AgCl reference and carbon counter electrodes on another piece of square paper after stacking. Using typical tris-(bipyridine)-ruthenium (Ⅱ) - tri-n-propylamine ECL system, the application test of this 3D paper-based ECL device was performed through the diagnosis of four tumor markers in real clinical serum samples. With the aid of a facile device-holder and a section-switch assembled on the analyzer, eight working electrodes were sequentially placed into the circuit to trigger the ECL reaction in the sweeping range from 0.5 to 1.1 V at room temperature. In addition, this 3D paper-based ECL device can be easily integrated and combined with the recently emerging paper electronics to further develop simple, sensitive, low-cost, disposable and portable μPAD for point-of-care testing, public health and environmental monitoring in remote regions, developing or developed countries. [Copyright &y& Elsevier]

Abstract: A novel lab-on-paper device combining the simplicity and low-cost of microfluidic paper-based analytical devices (μPADs) and the sensitivity and selectivity of chemiluminescence ELISA (CL-ELISA) for the high-throughput, rapid, stable and reusable point-of-care testing is presented here. Chitosan was used to modify μPADs to covalently immobilize antibodies on μPADs. Thus, sandwich CL-ELISA on μPADs can be easily realized for further development of this technique in sensitive, specific and low-cost application. The paper device was fabricated by a low-cost, simple, and rapid wax-screen-printing method. Using tumor markers and paper microzone plate as model, the application test of this paper-based CL-ELISA was successfully performed with a linear range of 0.1–35.0ngmL−1 for α-fetoprotein, 0.5–80.0UmL−1 for cancer antigen 125 and 0.1–70.0ngmL−1 for carcinoembryonic antigen. Since the cutoff values of the three tumor markers in clinical diagnosis are 25ngmL−1, 35UmL−1 and 5ngmL−1, the sensitivity and linear ranges of the proposed method were enough for clinical application. In addition, this lab-on-paper immunodevice can provide reproducible results upon storage at 4°C (sealed) for at least 5 weeks. Ultimately, this novel chitosan modification and wax-screen-printing methodology for μPADs can be readily translated to other signal reporting mechanism including electrochemiluminescence and photoelectrochemistry, and other receptors such as enzyme receptors and DNA receptors for determination of DNA, proteins and small molecules in point-of-care testing. [Copyright &y& Elsevier]