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We discuss the thermodynamics behind self-organizing Benzoquinone (BQ) particles on air–water interface. Experiments (Satterwhite-Warden et al., 2015; Chen et al., 2019; Satterwhite-Warden et al., 2019) reveal that BQ particles undergo rapid transient flocking behavior as they move around on the liquid surface. Flocks are seen to vary in size and their formation and stability appears to be dependent upon their shape. It is hypothesized that self organization of particles is a result of surface tension gradients in the two dimensional liquid surface resulting from the slow dissolution of the BQ particles. The current paper uses a mass-action kinetic framework to study the flocking of particles. Two dynamical models, with and without a reservoir, are proposed and analyzed through the thermodynamic lens of free energy, which informs us about dominant and spontaneous ‘reactions’ or flock formations in the system. Results of the model are in good agreement with experiment, revealing that irregular shaped BQ particles do indeed show far greater propensity to form flocks compared with regularly shaped particles and validating the mass-action framework as an appropriate tool to investigate this system.

We report a low-cost, sensitive, bead-based electrochemical immunoarray for soluble L-selectin (or CD62L protein), a potential biomarker for staging bladder cancer. We used a semi-automated modular microfluidic array with online antigen capture on superparamagnetic beads, which were subsequently delivered to a detection chamber housing multiple sensors. The assay was designed to accurately detect CD62L in diluted serum with a limit of detection (LOD) of 0.25 ng mL(−1) and a dynamic range of 0.25–100 ng mL(−1). The microfluidic array gave significantly better accuracy and higher sensitivity than a standard ELISA kit, which was shown to be subject to significant systematic error at high and low concentration ranges. 31 serum samples from patients with varying grades of bladder cancer and cancer-free controls were analyzed by the immunoarray and ELISA, and the CD62L levels correlated. This work establishes a new accurate assay for determining CD62L levels and highlights the potential of this protein as a biomarker for detecting locoregional progression of bladder cancer.

Collective self-motion of particulate systems provides novel opportunities for developing flocking and sensing functions from seemingly inanimate objects. In this paper, we report videos documenting spontaneous collective flocking of multiple irregularly shaped macroscopic benzoquinone (BQ) particles at the air-water interface. Self-propulsion occurs due to the Gibbs-Marangoni effect surface tension gradients generated by the BQ particles. The air-water interface develops inhomogeneous interfacial tension fields created by differential dissolution at points and edges of BQ particles, causing interfacial tension variations along the solid-liquid-air interfaces. Responses of irregularly shaped BQ particles to these driving forces do not result in random motion but lead to a cooperative hydrodynamic flocking. Curiously, the flocking behavior was very evident for irregularly shaped particles but not observed for symmetric circular BQ disks. The flock responds to changes in its local environment as it forages for interfacial free energy. It exhibits warm and cool thermotaxis and thus can sense local temperature changes. Also, though a single magnetic bead is not confined to a part of the Petri dish by an applied magnetic field, when this magnetic bead is a member of a flock in which all of the other beads are not magnetic, the flock as a whole moves and hovers around the region where the field is maximum. In other words, the magnetic bead becomes a kind of "sensor" for the flock to respond to a magnetic field, the response being a drift in the direction of the field.

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.

Clear plastic fluidic devices with ports for incorporating electrodes to enable electrochemiluminescence (ECL) measurements were prepared using a low-cost, desktop three-dimensional (3D) printer based on stereolithography. Electrodes consisted of 0.5 mm pencil graphite rods and 0.5 mm silver wires inserted into commercially available 1/4 in -28 threaded fittings. A bioimaging system equipped with a CCD camera was used to measure ECL generated at electrodes and small arrays using 0.2 M phosphate buffer solutions containing tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate ([Ru(bpy)(3)](2+)) with 100 mM tri-n-propylamine (TPA) as the coreactant. ECL signals produced at pencil graphite working electrodes were linear with respect to [Ru(bpy)(3)](2+) concentration for 9-900 mu M [Ru(bpy)(3)](2+). The detection limit was found to be 7 mu M using the CCD camera with exposure time set at 10 s. Electrode-to-electrode ECL signals varied by +/- 7.5%. Device performance was further evaluated using pencil graphite electrodes coated with multilayer poly(diallyldimethylammonium chloride) (PDDA)/DNA films. In these experiments, ECL resulted from the reaction of [Ru(bpy)(3)](3+) with guanines of DNA. ECL produced at these thin-film electrodes was linear with respect to [Ru(bpy)(3)](2+) concentration from 180 to 800 mu M. These studies provide the first demonstration of ECL measurements obtained using a 3D-printed closed-channel fluidic device platform. The affordable, high-resolution 3D printer used in these studies enables easy, fast, and adaptable prototyping of fluidic devices capable of incorporating electrodes for measuring ECL.

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.

Herein we report a low cost, sensitive, supercapacitor-powered electrochemiluminescent (ECL) protein immunoarray fabricated by an inexpensive 3-dimensional (3D) printer. The immunosensor detects three cancer biomarker proteins in serum within 35 min. The 3D-printed device employs hand screen printed carbon sensors with gravity flow for sample/reagent delivery and washing. Prostate cancer biomarker proteins, prostate specific antigen (PSA), prostate specific membrane antigen (PSMA) and platelet factor-4 (PF-4) in serum were captured on the antibody-coated carbon sensors followed by delivery of detection-antibody-coated Ru(bpy)3(2+) (RuBPY)-doped silica nanoparticles in a sandwich immunoassay. ECL light was initiated from RuBPY in the silica nanoparticles by electrochemical oxidation with tripropylamine (TPrA) co-reactant using supercapacitor power and ECL was captured with a CCD camera. The supercapacitor was rapidly photo-recharged between assays using an inexpensive solar cell. Detection limits were 300-500f gmL(-1) for the 3 proteins in undiluted calf serum. Assays of 6 prostate cancer patient serum samples gave good correlation with conventional single protein ELISAs. This technology could provide sensitive onsite cancer diagnostic tests in resource-limited settings with the need for only moderate-level training.