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Fingerprinting is an essential form of identification for both biometric security and forensics today. Herein, we describe the procedure and principle of creating highly resolved, chemically robust, 3D fingerprint physical replicas, which is based on the solvent-assisted molding of transparent plastics and motion-promoted growth of semi-crystalline polymeric nanostructures. Prior to fingerprinting atop, polycarbonate, a commercial polymer with excellent durability and optical transparency, is first swelled and softened with a mild solvent (acetone). The molding motion conforms polymer chains between fingerprint ridges, which facilitates the formation of semi-crystalline spherulites and results in greater opacity between ridges than underneath ridges. Besides being more enduring than digital scanning and ink printed counterparts, the plastic fingerprint replicas can provide additional morphological information (depth of the ridge) and high-level details (distribution of sweat pores).

We demonstrate herein an integrated, smartphone-app-chip (SPAC) system for on-site quantitation of food toxins, as demonstrated with aflatoxin B1 (AFB1), at parts-per-billion (ppb) level in food products. The detection is based on an indirect competitive immunoassay fabricated on a transparent plastic chip with the assistance of a microfluidic channel plate. A 3D-printed optical accessory attached to a smartphone is adapted to align the assay chip and to provide uniform illumination for imaging, with which high-quality images of the assay chip are captured by the smartphone camera and directly processed using a custom-developed Android app. The performance of this smartphone-based detection system was tested using both spiked and moldy corn samples; consistent results with conventional enzyme-linked immunosorbent assay (ELISA) kits were obtained. The achieved detection limit (3 ± 1 ppb, equivalent to μg/kg) and dynamic response range (0.5-250 ppb) meet the requested testing standards set by authorities in China and North America. We envision that the integrated SPAC system promises to be a simple and accurate method of food toxin quantitation, bringing much benefit for rapid on-site screening.

Fingerprint biometrics is a valuable and convenient security tool; every fingerprint is highly detailed and unique, we always have them on “hand”. Herein we describe a novel bench-top method of making 3D fingerprint replicas (namely, fingerprint phantoms) by exploring a unique microfabrication approach using conventional polymeric materials, to aid the development of reliable and accurate fingerprint biometrics. By pressing an impression of human fingerprints onto solvent-softened plastic plates (e.g., polycarbonate chips), followed by casting with polydimethylsiloxane (PDMS, a popular elastomer), we can produce a flexible, nanoscale detailed, 3D reproduction of the fingerprint (“phantom”). By testing with standard optical fingerprint scanners, we have shown that all three levels of fingerprint details can be precisely recorded and match well with the original fingerprint. Superior to artificial fingerprint patterns, these phantoms have the exact 3D features of fingerprints and introduce no variability compared to human sampling, which make them perfect targets for standardizing fingerprint scanners and for biometric applications. We envision that the microcontact replication protocol via unconventional PC molding promises a practical, bench-top, instrumentation-free method to mass reproduce many other micro/nanostructures with high fidelity.

A sensitive and cost-effective method for the simultaneous quantitation of trace amounts of Hg(2+) and Pb(2+) in real-world samples has been developed using DNA molecular beacon probes bound to bona fide digital video discs (DVDs). With specially designed T-rich or G-rich loop sequences, the detection is based on the strong T-Hg(2+)-T coordination chemistry of Hg(2+) and the formation of G-quadruplexes induced by Pb(2+), respectively. In particular, the presence of metal cations leads to hairpin opening and exposure of the terminal biotin moiety for binding nanogold-streptavidin conjugates. The recognition signal was subsequently enhanced by gold nanoparticle-promoted silver deposition, which leads to quantifiable digital signals upon reading with a standard computer drive. This method exhibits a wide response range and low detection limits for both Hg(2+) and Pb(2+). In addition, the quantitative determination of heavy metals in food products (e.g., rice samples) has been demonstrated and the method compares favorably with other optical sensors developed recently.

A demonstration for undergraduate teaching in upper-division physical chemistry and materials science courses is described. A simple protocol was developed to prepare superhydrophobic and hydrophobic glass by treating standard microscope slides with methyltrichlorosilane and octadecyltrichlorosilane, respectively. The unique wetting, optical, and self-cleaning properties of the modified surfaces can be demonstrated to students in class. Octadecyltrichlorosilane forms a closely packed, methyl-terminated, self-assembled monolayer that changes the glass surface from hydrophilic to hydrophobic; treatment with methyltrichlorosilane yields 3-dimensional polymethylsiloxane networked nanostructures, which leads to a superhydrophobic surface, that is, water droplets sit atop in the Cassie–Baxter state. In both cases, the glass slides maintain optical transparency despite remarkable changes in the surface wettability. A classroom demonstration of superhydrophobicity and self-cleaning using these surfaces, along wit...

We demonstrate a silanization reaction-based simple and reproducible method of converting a standard microscope glass slide to a transparent superhydrophobic surface with careful controlling of the temperature, concentration, and reaction time. By optimizing the preparation conditions, the two step treatment of a glass slide (reaction with dilute methyltrichlorosilane in toluene followed by ethanol extraction) leads to ultrahigh water contact angles (> 150°), i.e., water droplets sit atop the surface in the Cassie–Baxter state while the glass slide is still optically transparent. UV–vis absorption spectra confirm that the optical transmittance of the superhydrophobic glass slides can be as high as 99% (λ = 550 nm), which is superior to untreated slides (93%). Both the superhydrophobicity and optical transparency are dictated by the microscopic morphology resulting from the controlled silanization of the glass surface, for which in this study the reproducibility was achieved to be about 90%.

In this paper, we present a smartphone-readable barcode assay for the qualitative detection of methyl parathion residues, a toxic organophosphorus pesticide that is popularly used in agriculture worldwide. The detection principle is based on the irreversible inhibition of the enzymatic activity of acetylcholinesterase (AchE) by methyl parathion; AchE catalytically hydrolyzes acetylthiocholine iodine to thiocholine that in turn dissociates dithiobis-nitrobenzoate to produce a yellow product (deprotonated thio-nitrobenzoate). The yellow intensity of the product was confirmed to be inversely dependent on the concentration of the pesticide. We have designed a barcode-formatted assay chip by using a PDMS (polydimethylsiloxane) channel plate (as the reaction reservoir), situated under a printed partial barcode, to complete the whole barcode such that it can be directly read by a barcode scanning app installed on a smartphone. The app is able to qualitatively present the result of the pesticide test; the absence or a low concentration of methyl parathion results in the barcode reading as “−”, identifying the test as negative for pesticides. Upon obtaining a positive result (the app reads a “+” character), the captured image can be further analyzed to quantitate the methyl parathion concentration in the sample. Besides the portability and simplicity, this mobile-app based colorimetric barcode assay compares favorably with the standard spectrophotometric method.

The desire to develop new point-of-care (POC) diagnostic tools has led to the adaptation of smartphones to tackle limitations in state-of-the-art instrumentation and centralized laboratory facilities. Today’s smartphones possess the computer-like ability to image and process data using mobile apps; barcode scanners are one such type of apps. We demonstrate herein that a diagnostic assay can be performed by patterning immunoassay strips in a bona fide barcode format such that after target binding and signal enhancement, the linear barcode can be read directly with a standard smartphone app. Quantitative analysis can then be performed based on the grayscale intensities with a customized mobile app. This novel diagnostic concept has been validated for a real-world application, i.e., the detection of human chorionic gonadotropin, a pregnancy hormone. With the possibility of multiplex detection, the barcode assay protocol promises to boost POC diagnosis research by the direct adaptation of mobile devices and apps.

The feasibility of using smartphones and other mobile devices as the detection platform for quantitative scanometric assays is demonstrated. The different scanning modes (color, grayscale, black/white) and grayscale converting protocols (average, weighted average/luminosity, and software specific) have been compared in determining the optical darkness ratio (ODR) values, a conventional quantitation measure for scanometric assays. A mobile app was developed to image and analyze scanometric assays, as demonstrated by paper-printed tests and a biotin-streptavidin assay on a plastic substrate. Primarily for ODR analysis, the app has been shown to perform as well as a traditional desktop scanner, augmenting that smartphones (and other mobile devices) promise to be a practical platform for accurate, quantitative chemical analysis and medical diagnostics.

In this paper, we present a facile and cost-effective method to obtain superhydrophobic filter paper and demonstrate its application for efficient water/oil separation. By coupling structurally distinct organosilane precursors (e.g., octadecyltrichlorosilane and methyltrichlorosilane) to paper fibers under controlled reaction conditions, we have formulated a simple, inexpensive, and efficient protocol to achieve a desirable superhydrophobic and superoleophilic surface on conventional filter paper. The silanized superhydrophobic filter paper showed nanostructured morphology and demonstrated great separation efficiency (up to 99.4%) for water/oil mixtures. The modified filter paper is stable in both aqueous solutions and organic solvents, and can be reused multiple times. The present study shows that our newly developed binary silanization is a promising method of modifying cellulose-based materials for practical applications, in particular the treatment of industrial waste water and ecosystem recovery.