The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO 2 , a hazardous pollutant. We also use SiO 2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors.The fabrication of electronic devices on plastic substrates has attracted considerable recent attention owing to the proliferation of handheld, portable consumer electronics. Plastic substrates possess many attractive properties including biocompatibility, flexibility, light weight, shock resistance, softness and transparency [1][2][3] . However, most plastics deform or melt at temperatures of only 100−200 °C, placing severe limitations on the quality of semiconductors that can be grown directly on plastic. Central to continued advances in highperformance plastic electronics is the development of robust methods for overcoming this temperature restriction. Recently, three categories of approaches have emerged to address this problem.The first approaches are crystallization methods, in which an inferior inorganic semiconductor is vapour deposited at low temperatures onto plastic, and subsequently crystallized. An example is the conversion of amorphous silicon into polycrystalline silicon via laser crystallization 4 . Polysilicon thin-film transistors (TFTs) made in this way have yielded electron mobilities up to 250 cm 2 V −1 s −1 and hole mobilities up to 65 cm 2 V −1 s −1 (refs 5-7). However, this approach suffers from an inherent dichotomy between achieving high performance, which requires larger crystal grain sizes, and achieving homogeneity, which requires smaller grain sizes for uniformity in number of grain boundaries per © 2007 Nature Publishing Group * Correspondence and requests for materials should be addressed to J.R.H. heath@caltech.edu. Author contributions Competing financial interestsThe authors declare no competing financial interests. NIH Public Access TRANSFER OF NANOWIRES ONTO PLASTICThe dry transfer process uses the fact that the SNAP procedure is carried out on silicon-onoxide (SOI) wafers, as the buried silica can be readily etched to free the wires for transfer. Figure 1 summa...

Blood comprises the largest version of the human proteome1. Changes of plasma protein profiles can reflect physiological or pathological conditions associated with many human diseases, making blood the most important fluid for clinical diagnostics2-4. Nevertheless, only a handful of plasma proteins are utilized in routine clinical tests. This is due to a host of reasons, including the intrinsic complexity of the plasma proteome1, the heterogeneity of human diseases and the fast kinetics associated with protein degradation in sampled blood5. Simple technologies that can sensitively sample large numbers of proteins over broad concentration ranges, from small amounts of blood, and within minutes of sample collection, would assist in solving these problems. Herein, we report on an integrated microfluidic system, called the Integrated Blood Barcode Chip (IBBC). It enables on-chip blood separation and the rapid measurement of a panel of plasma proteins from small quantities of blood samples including a fingerprick of whole blood. This platform holds potential for inexpensive, non-invasive, and informative clinical diagnoses, particularly, for point-of-care.

Cellular immunity has an inherent high level of functional heterogeneity. Capturing the full spectrum of these functions requires analysis of large numbers of effector molecules from single cells. We report a microfluidic platform designed for highly multiplexed (more than ten proteins), reliable, sample-efficient (~1 × 104 cells) and quantitative measurements of secreted proteins from single cells. We validated the platform by assessment of multiple inflammatory cytokines from lipopolysaccharide (LPS)-stimulated human macrophages and comparison to standard immunotechnologies. We applied the platform toward the ex vivo quantification of T cell polyfunctional diversity via the simultaneous measurement of a dozen effector molecules secreted from tumor antigen–specific cytotoxic T lymphocytes (CTLs) that were actively responding to tumor and compared against a cohort of healthy donor controls. We observed profound, yet focused, functional heterogeneity in active tumor antigen–specific CTLs, with the major functional phenotypes quantitatively identified. The platform represents a new and informative tool for immune monitoring and clinical assessment.