A three-dimensional electrochemical paper-based analytical device for low-cost diagnostics.

Paper-based microfluidic devices with screen-printed electrodes (SPEs) for electrochemical sensing are popular for low-cost point-of-care diagnostics. The electroactive sensing area in these devices is always the irregular, bottom-SPE surface which is in contact with the analyte flowing within the paper substrate. Unfortunately, this results in an electroactive area which varies widely from sensor to sensor. In this paper, we present a three-dimensional paper-based analytical device with a hollow 3D fluid reservoir which allows for use of a more uniform top-SPE surface as the electroactive sensing area. The use of this isolated reservoir eliminates the need for dielectric inks used in conventional SPEs on paper. Our sensors are fabricated using a combination of wax-printing, screen-printing and simple folding via a cleanroom free process without the need for expensive equipment. Additionally, for the first time, we demonstrate an electrochemical paper-based analytical device with a custom designed potentiostat integrated circuit (IC) as a miniaturized reader. The versatility of the sensor is demonstrated through voltammetric, amperometric and potentiometric measurements of important biochemical analytes such as dopamine, glucose and pH. The 3D ePAD together with a custom CMOS potentiostat demonstrates a low-cost, versatile, self-contained system suitable for point-of-care diagnostic devices.

Viral-templated gold/polypyrrole nanopeapods for an ammonia gas sensor.

One-dimensional gold/polypyrrole (Au/PPy) nanopeapods were fabricated using a viral template: M13 bacteriophage. The genetically modified filamentous virus displayed gold-binding peptides along its length, allowing selective attachment of gold nanoparticles (Au NPs) under ambient conditions. A PPy shell was electropolymerized on the viral-templated Au NP chains forming nanopeapod structures. The PPy shell morphology and thickness were controlled through electrodeposition potential and time, resulting in an ultra-thin conductive polymer shell of 17.4 ± 3.3 nm. A post-electrodeposition acid treatment was used to modify the electrical properties of these hybrid materials. The electrical resistance of the nanopeapods was monitored at each assembly step. Chemiresistive ammonia (NH3) gas sensors were developed from networks of the hybrid Au/PPy nanostructures. Room temperature sensing performance was evaluated from 5 to 50 ppmv and a mixture of reversible and irreversible chemiresistive behavior was observed. A sensitivity of 0.30%/ppmv was found for NH3 concentrations of 10 ppmv or less, and a lowest detection limit (LDL) of 0.007 ppmv was calculated. Furthermore, acid-treated devices exhibited an enhanced sensitivity of 1.26%/ppmv within the same concentration range and a calculated LDL of 0.005 ppmv.

Highly sensitive hydrogen sulfide (H2S) gas sensors from viral-templated nanocrystalline gold nanowires.

A facile, site-specific viral-templated assembly method was used to fabricate sensitive hydrogen sulfide (H2S) gas sensors at room temperature. A gold-binding M13 bacteriophage served to organize gold nanoparticles into linear arrays which were used as seeds for subsequent nanowire formation through electroless deposition. Nanowire widths and densities within the sensors were modified by electroless deposition time and phage concentration, respectively, to tune device resistance. Chemiresistive H2S gas sensors with superior room temperature sensing performance were produced with sensitivity of 654%/ppm(v), theoretical lowest detection limit of 2 ppb(v), and 70% recovery within 9 min for 0.025 ppm(v). The role of the viral template and associated gold-binding peptide was elucidated by removing organics using a short O2 plasma treatment followed by an ethanol dip. The template and gold-binding peptide were crucial to electrical and sensor performance. Without surface organics, the resistance fell by several orders of magnitude, the sensitivity dropped by more than a factor of 100 to 6%/ppm(v), the lower limit of detection increased, and no recovery was detected with dry air flow. Viral templates provide a novel, alternative fabrication route for highly sensitive, nanostructured H2S gas sensors.

Phage-directed synthesis of copper sulfide: structural and optical characterization.

The growth of crystalline copper sulfide using a viral template was investigated using sequential incubation in CuCl2 and Na2S precursors. Non-specific electrostatic attraction between a genetically-modified M13 bacteriophage and copper cations in the CuCl2 precursor caused phage agglomeration and bundle formation. Following the addition of Na2S, polydisperse nanocrystals 2-7 nm in size were found along the length of the viral scaffold. The structure of the copper sulfide material was identified as cubic anti-fluorite type Cu1.8S, space group Fm3[overline]m. Strong interband absorption was observed within the ultraviolet to visible range with an onset near 800 nm. Furthermore, free carrier absorption, associated with the localized surface plasmon resonance of the copper sulfide nanocrystals, was seen in the near infrared with absorbance maxima at 1060 nm and 3000 nm, respectively.

alpha-Synuclein enhances bioluminescent activity of firefly luciferase by facilitating luciferin localization.

alpha-Synuclein, the pathological component of Parkinson's disease, has been demonstrated to be highly interactive with various protein partners. alpha-Synuclein has been shown to exert a novel effect on the bioluminescence of firefly luciferase by stimulating the oxyluciferin formation from its substrate of luciferin, which results in a significant enhancement of the spike of flashing light via concomitant augmentation for both rapid rise and quick decay of the luminescence. Binding affinity between alpha-synuclein and luciferase was evaluated with K(d) of 8.1 microM based on a dose-dependent enhancement of the luciferase activity by alpha-synuclein. Kinetic analyses indicated that alpha-synuclein has facilitated luciferin localization to the luciferase by decreasing apparent K(m), which makes the maximum rate of bioluminescence no longer dependent upon ATP concentration. Catalytic consequences of the alpha-synuclein binding to luciferase have led to a delayed onset of the coenzyme A-mediated retardation of the quick decay of flashing light as well as a shift in the emission spectra of bioluminescence. Taken together, the novel effects of alpha-synuclein toward the bioluminescence of luciferase have been demonstrated to be initiated by the specific molecular interaction between the proteins which has influenced the substrate (luciferin) localization to the enzyme.