José L. García-Cordero

We present a self-powered integrated microfluidic blood analysis system (SIMBAS) that does not require any external connections, tethers, or tubing to deliver and analyze a raw whole-blood sample. SIMBAS only requires the user to place a 5 μL droplet of whole-blood at the inlet port of the device, whereupon the stand-alone SIMBAS performs on-chip removal of red and white cells, without external valving or pumping mechanisms, followed by analyte detection in platelet-containing plasma. Five complete biotin-streptavidin sample-to-answer assays are performed in 10 min; the limit of detection is 1.5 pM. Red and white blood cells are removed by trapping them in an integral trench structure. Simulations and experimental data show 99.9% to 100% blood cell retention in the passive structure. Powered by pre-evacuation of its PDMS substrate, SIMBAS' guiding design principle is the integration of the minimal number of components without sacrificing effectiveness in performing rapid complete bioassays, a critical step towards point-of-care molecular diagnostics.

Label-free biosensing based on metallic nanoparticles supporting localized surface plasmon resonances (LSPR) has recently received growing interest (Anker, J. N., et al. Nat. Mater. 2008, 7, 442-453). Besides its competitive sensitivity (Yonzon, C. R., et al. J. Am. Chem. Soc. 2004, 126, 12669-12676; Svendendahl, M., et al. Nano Lett. 2009, 9, 4428-4433) when compared to the surface plasmon resonance (SPR) approach based on extended metal films, LSPR biosensing features a high-end miniaturization potential and a significant reduction of the interrogation device bulkiness, positioning itself as a promising candidate for point-of-care diagnostic and field applications. Here, we present the first, paralleled LSPR lab-on-a-chip realization that goes well beyond the state-of-the-art, by uniting the latest advances in plasmonics, nanofabrication, microfluidics, and surface chemistry. Our system offers parallel, real-time inspection of 32 sensing sites distributed across 8 independent microfluidic channels with very high reproducibility/repeatability. This enables us to test various sensing strategies for the detection of biomolecules. In particular we demonstrate the fast detection of relevant cancer biomarkers (human alpha-feto-protein and prostate specific antigen) down to concentrations of 500 pg/mL in a complex matrix consisting of 50% human serum.

The vast majority of microfluidic systems are molded in poly(dimethylsiloxane) (PDMS) by soft lithography due to the favorable properties of PDMS: biocompatible, elastomeric, transparent, gas-permeable, inexpensive, and copyright-free. However, PDMS molding involves tedious manual labor, which makes PDMS devices prone to assembly failures and difficult to disseminate to research and clinical settings. Furthermore, the fabrication procedures limit the 3D complexity of the devices to layered designs. Stereolithography (SL), a form of 3D-printing, has recently attracted attention as a way to customize the fabrication of biomedical devices due to its automated, assembly-free 3D fabrication, rapidly decreasing costs, and fast-improving resolution and throughput. However, existing SL resins are not biocompatible and patterning transparent resins at high resolution remains difficult. Here we report procedures for the preparation and patterning of a transparent resin based on low-MW poly(ethylene glycol) diacrylate (MW 250) (PEG-DA-250). The 3D-printed devices are highly transparent and cells can be cultured on PEG-DA-250 prints for several days. This biocompatible SL resin and printing process solves some of the main drawbacks of 3D-printed microfluidic devices: biocompatibility and transparency. In addition, it should also enable the production of non-microfluidic biomedical devices.

We demonstrate the first integrated microfluidic tmRNA purification and nucleic acid sequence-based amplification (NASBA) device incorporating real-time detection. The real-time amplification and detection step produces pathogen-specific response in < 3 min from the chip-purified RNA from 100 lysed bacteria. On-chip RNA purification uses a new silica bead immobilization method. On-chip amplification uses custom-designed high-selectivity primers and real-time detection uses molecular beacon fluorescent probe technology; both are integrated on-chip with NASBA. Present in all bacteria, tmRNA (10Sa RNA) includes organism-specific identification sequences, exhibits unusually high stability relative to mRNA, and has high copy number per organism; the latter two factors improve the limit of detection, accelerate time-to-positive response, and suit this approach ideally to the detection of small numbers of bacteria. Device efficacy was demonstrated by integrated on-chip purification, amplification, and real-time detection of 100 E. coli bacteria in 100 microL of crude lysate in under 30 min for the entire process.

Sessile droplets are non-movable droplets spanning volumes in the nL-to-μL range. The sessile-droplet-based platform provides a paradigm shift from the conventional, flow-based lab-on-a-chip philosophy, yet offering similar benefits: low reagent/sample consumption, high throughput, automation, and most importantly flexibility and versatility. Moreover, the platform relies less heavily on sophisticated fabrication techniques, often sufficient with a hydrophobic substrate, and no pump is required for operation. In addition, exploiting the physical phenomena that naturally arise when a droplet evaporates, such as the coffee-ring effect or Marangoni flow, can lead to fascinating applications. In this review, we introduce the physics of droplets, and then focus on the different types of chemical and biological assays that have been implemented in sessile droplets, including analyte concentration, particle separation and sorting, cell-based assays, and nucleic acid amplification. Finally, we provide our perspectives on this unique micro-scale platform.