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In this work, we fabricated a novel origami paper-based analytical device (oPAD) assisted by the nanostructuring effect of in situ Pd decoration of Cu/Co-doped CeO2 (CuCo-CeO2-Pd) nanospheres, functionalized with their strongly enhanced electrocatalytic properties to realize an electrochemical and visual signal readout system in oPAD, for highly sensitive detection of amyloid-β (Aβ). The CuCo-CeO2-Pd nanospheres were introduced as an enhanced "signal transducer layer" on account of the electron transfer acceleration caused by catalyzing glucose to produce H2O2 for differential pulse voltammetry signal readout and further 3,3'5,5'-tetramethylbenzidine (TMB) oxidation for colorimetric analysis. Meanwhile, for achieving superior performance of the proposed oPAD, in situ growth of urchin-like gold nanoparticles (Au NPs) onto cellulose fibers was adopted to improve "the recognition layer" in favor of immobilizing antibodies for targeting Aβ through specific antigen-antibody interactions. Combined with the delicate design of oPAD, exhibiting actuation of the conversion procedure between hydrophobicity and hydrophilicity on paper tabs in the assay process, the oPAD successfully enabled sensitive diagnosis of Aβ in a linear range from 1.0 pM to 100 nM with a limit of detection of 0.05 pM (S/N = 3) for electrochemical detection, providing a reliable strategy for quantifying the Aβ protein in clinical applications. Ministry of Education (MOE) This work was financially supported by the Science and Technology Projects of University of Jinan (XKY2002), the Natural Science Foundation of Shandong Province (ZR2020MB057), the Singapore Ministry of Education (MOE AcRF Tier 1 RG176/16), the Taishan Scholars Program, the Case-by-Case Project for Top Outstanding Talents of Jinan, and the project of "20 Items of University" of Jinan (2018GXRC001).

Isothermal amplification strategies capable of rapid, inexpensive, and accurate nucleic acid detection provide new options for large-scale pathogen detection, disease diagnosis, and genotyping. Here we report a highly sensitive multicomponent XNA-based nucleic acid detection platform that combines analyte preamplification with X10-23-mediated catalysis to detect the viral pathogen responsible for COVID-19. The platform, termed RNA-Encoded Viral Nucleic Acid Analyte Reporter (REVEALR), functions with a detection limit of ≤20 aM (∼10 copies/μL) using conventional fluorescence and paper-based lateral flow readout modalities. With a total assay time of 1 h, REVEALR provides a convenient nucleic acid alternative to equivalent CRISPR-based approaches, which have become popular methods for SARS-CoV-2 detection. The assay shows no cross-reactivity for other in vitro transcribed respiratory viral RNAs and functions with perfect accuracy against COVID-19 patient-derived clinical samples.

The development of low cost, portable, and disposable biosensors for equipment-free and naked-eye biosensing is in eager demand for their widespread application in biomedical field, but it is still a challenge. Herein, we propose a novel paper analytical device (PAD) for truly equipment-free and naked-eye biosensing using dopamine as the chromogenic agent based on target-initiated catalyzed oxidation reaction. The dopamine-functionalized PAD (DPAD) possesses a significant three-dimensional net structure, excellent hydrophilicity, and unique response toward G-quadruplex DNAs against other DNAs, benefiting the bio/chemo reaction occurrence to assay target biomolecules. In light of the exceptional properties, the fabricated DPAD was applied in the analysis of Dam MTase through target-triggered exponential isothermal amplification. The recognition and methylation of H1 by Dam MTase contribute to formation of abundant hemin/G-quadruplexes, which catalyze oxidation of dopamine into dopachrome and reduce the dopamine amount on the DPAD surface. In comparison with the case in which Dam MTase is absent, an evident deep pink signal originating from dopachrome is observed directly by the naked eye and relied on Dam MTase concentrations. Therefore, truly equipment-free and naked-eye detection of Dam MTase is achieved with a detection limit of 1.46 U/mL. The fabricated DPAD not only achieves Dam MTase-visualized detection but also permits the accurate determination of other analytes by varying recognizable DNA's sequences, thus offering a universal biosensor and depicting significant potential for widespread applications in biomedical field.

Current analytical methods, either point-of-care or centralized detection, are not able to meet recent demands of patient-friendly testing and increased reliability of results. Here, we describe a two-point separation on-demand diagnostic strategy based on a paper-based mass spectrometry immunoassay platform that adopts stable and cleavable ionic probes as mass reporter; these probes make possible sensitive, interruptible, storable, and restorable on-demand detection. In addition, a new touch paper spray method was developed for on-chip, sensitive, and cost-effective analyte detection. This concept is successfully demonstrated via (i) the detection of Plasmodium falciparum histidine-rich protein 2 antigen and (ii) multiplexed and simultaneous detection of cancer antigen 125 and carcinoembryonic antigen.

DNA analysis is essential for diagnosis and monitoring of many diseases. Conventional DNA testing is generally limited to the laboratory. Increasing access to relevant technologies can improve patient care and outcomes in both developed and developing regions. Here, we demonstrate direct DNA analysis in paper-based devices, uniquely enabled by ion concentration polarization at the interface of patterned nanoporous membranes in paper (paper-based ICP). Hepatitis B virus DNA targets in human serum are simultaneously preconcentrated, separated, and detected in a single 10 min operation. A limit of detection of 150 copies/mL is achieved without prior viral load amplification, sufficient for early diagnosis of hepatitis B. We clinically assess the DNA integrity of sperm cells in raw human semen samples. The percent DNA fragmentation results from the paper-based ICP devices strongly correlate (R(2) = 0.98) with the sperm chromatin structure assay. In all cases, agreement was 100% with respect to the clinical decision. Paper-based ICP can provide inexpensive and accessible advanced molecular diagnostics.

Titanium dioxide (TiO2) photocatalyst and zeolite adsorbent were made into a paper-like composite by a papermaking technique using pulp and ceramic fibers as sheet matrix. The photocatalytic performance for the degradation of bisphenol A (BPA) dissolved in water was investigated under UV irradiation. The TiO2 sheet prepared was easier to handle than the original TiO2 powders in aqueous media. The TiO2 sheet could decompose the BPA under UV irradiation, although at a lower degradation efficiency than the TiO2 suspension. The TiO2-free zeolite sheet could not remove the BPA from water completely because of its adsorption equilibrium. Furthermore, the composite TiO2-zeolite sheets exhibited a higher efficiency for BPA removal than the zeolite-free TiO2 sheets, the efficiency of the former being equivalent to that of the TiO2 suspension. The enhancement in removal efficiency was not attributed to the simple adsorption of BPA on zeolite but rather to the synergistic effect obtained through the combined use of TiO2 photocatalyst and zeolite adsorbent in the paper-like composite sheet, which is believed to accelerate the BPA photodegradation in water.

We report a method, based on the principles of origami (paper folding), for fabricating three-dimensional (3-D) paper microfluidic devices. The entire 3-D device is fabricated on a single sheet of flat paper in a single photolithographic step. It is assembled by simply folding the paper by hand. Following analysis, the device can be unfolded to reveal each layer. The applicability of the device to chemical analysis is demonstrated by colorimetric and fluorescence assays using multilayer microfluidic networks.

Surface sol-gel process was used to replicate the hierarchical morphology of natural cellulosic substances with nanometer precision. The resultant artificial fossils are ceramic nanomaterials composed of metal oxide nanotubes.