Gregory W. Bishop

3D-Printed Fluidic Devices for Nanoparticle Preparation and Flow-Injection Amperometry Using Integrated Prussian Blue Nanoparticle-Modified Electrodes

A consumer-grade fused filament fabrication (FFF) 3D printer was used to construct fluidic devices for nanoparticle preparation and electrochemical sensing. Devices were printed using poly(ethylene terephthalate) and featured threaded ports to connect polyetheretherketone (PEEK) tubing via printed fittings prepared from acrylonitrile butadiene styrene (ABS). These devices included channels designed to have 800 μm × 800 μm square cross sections and were semitransparent to allow visualization of the solution-filled channels. A 3D-printed device with a Y-shaped mixing channel was used to prepare Prussian blue nanoparticles (PBNPs) under flow rates of 100 to 2000 μL min(-1). PBNPs were then attached to gold electrodes for hydrogen peroxide sensing. 3D-printed devices used for electrochemical measurements featured threaded access ports into which a fitting equipped with reference, counter, and PBNP-modified working electrodes could be inserted. PBNP-modified electrodes enabled amperometric detection of H2O2 in the 3D-printed channel by flow-injection analysis, exhibiting a detection limit of 100 nM and linear response up to 20 μM. These experiments show that a consumer-grade FFF printer can be used to fabricate low-cost fluidic devices for applications similar to those that have been reported with more expensive 3D-printing methods.

Electroosmotic Flow Rectification in Pyramidal-Pore Mica Membranes

We demonstrate here a new electrokinetic phenomenon, Electroosmotic flow (EOF) rectification, in synthetic membranes containing asymmetric pores. Mica membranes with pyramidally shaped pores prepared by the track-etch method were used. EOF was driven through these membranes by using an electrode in solutions on either side to pass a constant ionic current through the pores. The velocity of EOF depends on the polarity of the current. A high EOF velocity is obtained when the polarity is such that EOF is driven from the larger base opening to the smaller tip opening of the pore. A smaller EOF velocity is obtained when the polarity is reversed such that EOF goes from tip to base. We show that this rectified EOF phenomenon is the result of ion current-rectification observed in such asymmetric-pore membranes.

Resistive-Pulse Measurements with Nanopipettes: Detection of Vascular Endothelial Growth Factor C (VEGF-C) Using Antibody-Decorated Nanoparticles

Quartz nanopipettes have recently been employed for resistive-pulse sensing of Au nanoparticles (AuNP) and nanoparticles with bound antibodies. The analytical signal in such experiments is the change in ionic current caused by the nanoparticle translocation through the pipette orifice. This paper describes resistive-pulse detection of cancer biomarker (Vascular Endothelial Growth Factor-C, VEGF-C) through the use of antibody-modified AuNPs and nanopipettes. The main challenge was to differentiate between AuNPs with attached antibodies for VEGF-C and antigen-conjugated particles. The zeta-potentials of these types of particles are not very different, and, therefore, carefully chosen pipettes with well-characterized geometry were necessary for selective detection of VEGF-C.

Catalytic Reduction of 1,1,1-Trichloro-2,2,2-trifluoroethane (CFC-113a) by Cobalt(I) Salen Electrogenerated at Vitreous Carbon Cathodes in Dimethylformamide

Catalytic reduction of 1,1,1-trichloro-2,2,2-trifluoroethane (CFC-113a or Freon 113a) by cobalt(I) salen electrogenerated at a carbon cathode in dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF 4 ) has been investigated with the aid of cyclic voltammetry, controlled-potential electrolysis, gas chromatography-mass spectrometry, and high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS). Cyclic voltammetry reveals that CFC-113a and two of its degradation products, 2,2-dichloro-l,l,l-trifluoroethane (HCFC-123) and 2-chloro-1,1,1-trifluoroethane (HCFC-133a), can all undergo catalytic reduction by cobalt(I) salen. Controlled-potential (bulk) electrolyses of cobalt(II) salen in the presence of CFC-113a lead to the production of HCFC-123, HCFC-133a, 2-chloro-l,l-difluoroethene (HCFC-1122), and 1,1-difluoroethene (HFC-1132a). HPLC-ESI-MS has been employed to demonstrate that, during the bulk catalytic reduction of CFC- 113a, the salen ligand of the catalyst is modified through addition of a CF 3 CCl 2 - or CF 3 CHCl- moiety to an imino (C = N) bond. On the basis of documented knowledge about the electrochemistry of cobalt-containing complexes, together with the results of our cyclic voltammetry and bulk electrolysis experiments, a mechanistic scheme is proposed for the cobalt(I) salen-catalyzed reduction of CFC-113a.

Fe3O4 nanoparticles on graphene oxide sheets for isolation and ultrasensitive amperometric detection of cancer biomarker proteins

Ultrasensitive mediator-free electrochemical detection for biomarker proteins was achieved at low cost using a novel composite of Fe3O4 nanoparticles loaded onto graphene oxide (GO) nano-sheets (Fe3O4@GO). This paramagnetic Fe3O4@GO composite (1µm size range) was decorated with antibodies against prostate specific antigen (PSA) and prostate specific membrane antigen (PSMA), and then used to first capture these biomarkers and then deliver them to an 8-sensor detection chamber of a microfluidic immunoarray. Screen-printed carbon sensors coated with electrochemically reduced graphene oxide (ERGO) and a second set of antibodies selectively capture the biomarker-laden Fe3O4@GO particles, which subsequently catalyze hydrogen peroxide reduction to detect PSA and PSMA. Accuracy was confirmed by good correlation between patient serum assays and enzyme-linked immuno-sorbent assays (ELISA). Excellent detection limits (LOD) of 15 fg/mL for PSA and 4.8 fg/mL for PSMA were achieved in serum. The LOD for PSA was 1000-fold better than the only previous report of PSA detection using Fe3O4. Dynamic ranges were easily tunable for concentration ranges encountered in serum samples by adjusting the Fe3O4@GO Concentration. Reagent cost was only

3D-printed bioanalytical devices

0.85 for a single 2-protein assay.

Low-cost photolithographic fabrication of nanowires and microfilters for advanced bioassay devices.

While 3D printing technologies first appeared in the 1980s, prohibitive costs, limited materials, and the relatively small number of commercially available printers confined applications mainly to prototyping for manufacturing purposes. As technologies, printer cost, materials, and accessibility continue to improve, 3D printing has found widespread implementation in research and development in many disciplines due to ease-of-use and relatively fast design-to-object workflow. Several 3D printing techniques have been used to prepare devices such as milli- and microfluidic flow cells for analyses of cells and biomolecules as well as interfaces that enable bioanalytical measurements using cellphones. This review focuses on preparation and applications of 3D-printed bioanalytical devices.

Low Cost 3D-Printed Biosensor Arrays for Protein-based Cancer Diagnostics based on Electrochemiluminescence

Integrated microfluidic devices with nanosized array electrodes and microfiltration capabilities can greatly increase sensitivity and enhance automation in immunoassay devices. In this contribution, we utilize the edge-patterning method of thin aluminum (Al) films in order to form nano- to micron-sized gaps. Evaporation of high work-function metals (i.e., Au, Ag, etc.) on these gaps, followed by Al lift-off, enables the formation of electrical uniform nanowires from low-cost, plastic-based, photomasks. By replacing Al with chromium (Cr), the formation of high resolution, custom-made photomasks that are ideal for low-cost fabrication of a plurality of array devices were realized. To demonstrate the feasibility of such Cr photomasks, SU-8 micro-pillar masters were formed and replicated into PDMS to produce micron-sized filters with 3–4 µm gaps and an aspect ratio of 3. These microfilters were capable of retaining 6 µm beads within a localized site, while allowing solvent flow. The combination of nanowire arrays and micro-pillar filtration opens new perspectives for rapid R&D screening of various microfluidic-based immunoassay geometries, where analyte pre-concentration and highly sensitive, electrochemical detection can be readily co-localized.

3D Printed Microfluidic Devices

Development and fabrication of bioanalytical devices by 3D printing offers revolutionary new routes to low cost clinical diagnostic devices for molecular measurements. Relevant to future protein-based cancer diagnostics, we describe and review here our recent development of prototype protein immunoarray devices using desktop Fused Deposition Modeling (FDM) and stereolithographic 3D printers. All these system feature sensitive electro-optical detection by a method called electrochemiluminescence (ECL). Our first 3D-printed immunoarray features screen-printed sensors in which manual manipulations enable gravity flow reagent delivery for measurement of 3 proteins at detection limits of 0.3 to 0.5 pg/mL. ECL detection is achieved in an open channel on integrated disposable screen-printed sensor elements. We then address the issue of printing and processing optically clear plastic using a stereolithographic printer to build a closed ECL detection chamber. Finally, we describe a prototype 3D-printed microprocessor-controlled enclosed microfluidic ECL immunoarray featuring reagent reservoirs, micropumps and clear plastic detection chamber with printed nanowells for ECL emission.

Resistive-Pulse Studies of Proteins and Protein/Antibody Complexes Using a Conical Nanotube Sensor

3D printing has recently emerged as an intriguing method for producing microfluidic devices due to its simple operation and fast design-to-object workflow. Advances and growing interest in 3D printing technologies have improved affordability and accessibility of printers and printing materials, further accelerating the pace of innovation. 3D printing has been used to prepare molds for poly(dimethylsiloxane) (PDMS)-based microfluidics, scaffolds for microvasculature networks, and directly printed fluidic devices that have been incorporated into biosensing platforms and systems for cell studies. While many 3D printing techniques lack the resolution to prepare truly microscale features at present, the rapidly developing nature of the technologies and a groundswell of interest in their applications are poised to drive improvements necessary to make 3D printing a reliable and routine strategy for producing microfluidic devices. Here, technical aspects of 3D printing methods and applications of 3D-printed microfluidic devices in biosensing are summarized.