Paper works: Paper‐based indirect ELISA (see picture) has been demonstrated through the detection of rabbit IgG and the HIV‐1 envelope antigen gp41. This technique combines the sensitivity and specificity of ELISA with the low cost and ease‐of‐use of paper‐based platforms.

Electrically−transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high−performance electricallytransduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electricallytransduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure−property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

This paper describes the synthesis of a novel intrinsically conductive two-dimensional (2D) covalent organic framework (COF) through the aromatic annulation of 2,3,9,10,16,17,23,24-octa-aminophthalocyanine nickel­(II) and pyrene-4,5,9,10-tetraone. The intrinsic bulk conductivity of the COF material (termed COF-DC-8) reached 2.51 × 10–3 S/m, and increased by 3 orders of magnitude with I2 doping. Electronic calculations revealed an anisotropic band structure, with the possibility for significant contribution from out-of-plane charge-transport to the intrinsic bulk conductivity. Upon integration into chemiresistive devices, this conductive COF showed excellent responses to various reducing and oxidizing gases, including NH3, H2S, NO, and NO2, with parts-per-billion (ppb) limits of detection (for NH3 = 70 ppb, for H2S = 204 ppb, for NO = 5 ppb, and for NO2 = 16 ppb based on 1.5 min exposure). Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy studies suggested that the chemiresistive response of the COF-DC-8 involves charge transfer interactions between the analyte and nickelphthalocyanine component of the framework.

Two-dimensional (2D) conductive metal-organic frameworks (MOFs) have emerged as a unique class of multifunctional materials due to their compositional and structural diversity accessible through bottom-up self-assembly. This feature article summarizes the progress in the development of 2D conductive MOFs with emphasis on synthetic modularity, device integration strategies, and multifunctional properties. Applications spanning sensing, catalysis, electronics, energy conversion, and storage are discussed. The challenges and future outlook in the context of molecular engineering and practical development of 2D conductive MOFs are addressed.

This paper describes an analytical system that uses magnetic levitation to measure densities of solids and water-immiscible organic liquids with accuracies ranging from +/-0.0002 to +/-0.02 g/cm(3), depending on the type of experiment. The technique is compatible with densities of 0.8-3 g/cm(3) and is applicable to samples with volumes of 1 pL to 1 mL; the samples can be either spherical or irregular in shape. The method employs two permanent NdFeB magnets positioned with like poles facing one another--with the axis between the poles aligned with the gravitational field--and a container filled with paramagnetic medium (e.g., MnCl(2) dissolved in water) placed between these magnets. Density measurements are obtained by placing the sample into the container and measuring the position of the sample relative to the bottom magnet. The balance of magnetic and gravitational forces determines the vertical position of the sample within the device; knowing this position makes it possible to calculate the density of the sample.

This article describes a point-of-care (POC) system--comprising a microfluidic, paper-based analytical device (micro-PAD) and a hand-held optical colorimeter--for quantifying the concentration of analytes in biological fluids. The micro-PAD runs colorimetric assays, and consists of paper that has been (i) patterned to expose isolated regions of hydrophilic zones and (ii) wet with an index-matching fluid (e.g., vegetable oil) that is applied using a disposable, plastic sleeve encasement. Measuring transmittance through paper represents a new method of quantitative detection that expands the potential functionality of micro-PADs. This prototype transmittance colorimeter is inexpensive, rugged, and fully self-contained, and thus potentially attractive for use in resource-limited environments and developing countries.

This paper describes the first demonstration of using a series of isoreticular nickel phthalocyanine- and nickel naphthalocyanine-based bimetallic conductive two-dimensional (2D) metal–organic frameworks (MOFs) as active materials in chemiresistive sensing of gases. Devices achieve exceptional sensitivity at sub-part-per-million (ppm) to part-per-billion (ppb) detection limits toward NH3 (0.31–0.33 ppm), H2S (19–32 ppb), and NO (1.0–1.1 ppb) at low driving voltages (0.01–1.0 V) within 1.5 min of exposure. The devices maintain their performance in the presence of humidity (5000 ppm of H2O). The isoreticular analogs enable modular control over selectivity and sensitivity in gas sensing through different combinations of linkers and metal nodes. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy studies suggest that the chemiresistive response of the MOFs involves charge transfer interactions triggered by the analytes adsorbed on MOFs.

This paper describes a paper-based microfluidic device that measures two enzymatic markers of liver function (alkaline phosphatase ALP, and aspartate aminotransferase AST) and total serum protein. A device consists of four components: i) a top plastic sheet, ii) a filter membrane, iii) a patterned paper chip containing the reagents necessary for analysis, and iv) a bottom plastic sheet. The device performs both the sample preparation (separating blood plasma from erythrocytes) and the assays; it also enables both qualitative and quantitative analysis of data. The data obtained from the paper-microfluidic devices show standard deviations in calibration runs and “spiked” standards that are acceptable for routine clinical use. This device illustrates a type of test useable for a range of assays in resource-poor settings.