Publications

'Peltier Couple' published in 'Encyclopedia of Nanotechnology'

Semiconductor nanowires and other one-dimensional materials are attractive for highly sensitive and spatially confined electrical and optical signal detection in biological and physical systems, although it has been difficult to localize active electronic or optoelectronic device function at one end of such one-dimensional structures. Here we report a new nanowire structure in which the material and dopant are modulated specifically at only one end of nanowires to encode an active two-terminal device element. We present a general bottom-up synthetic scheme for these tip-modulated nanowires and illustrate this with the synthesis of nanoscale p–n junctions. Electron microscopy imaging verifies the designed p-Si nanowire core with SiO2 insulating inner shell and n-Si outer shell with clean p-Si/n-Si tip junction. Electrical transport measurements with independent contacts to the p-Si core and n-Si shell exhibited a current rectification behavior through the tip and no detectable current through the SiO2 shell. Electrical measurements also exhibited an n-type response in conductance versus water-gate voltage with pulsed gate experiments yielding a temporal resolution of at least 0.1 ms and ∼90% device sensitivity localized to within 0.5 μm from the nanowire p–n tip. In addition, photocurrent experiments showed an open-circuit voltage of 0.75 V at illumination power of ∼28.1 μW, exhibited linear dependence of photocurrent with respect to incident illumination power with an estimated responsivity up to ∼0.22 A/W, and revealed localized photocurrent generation at the nanowire tip. The tip-modulated concept was further extended to a top-down/bottom-up hybrid approach that enabled large-scale production of vertical tip-modulated nanowires with a final synthetic yield of >75% with >4300 nanowires. Vertical tip-modulated nanowires were fabricated into >50 individually addressable nanowire device arrays showing diode-like current–voltage characteristics. These tip-modulated nanowire devices provide substantial opportunity in areas ranging from biological and chemical sensing to optoelectronic signal and nanoscale photodetection.

Background: Being physically active has been associated with lower risks of cardiometabolic diseases. However, the biological mechanisms underlying these associations remain unclear, and can be investigated using a metabolomics approach. Objective: To identify plasma metabolites associated with habitual physical activity in a U.S. population. Methods: Our study population included 4119 participants in the Nurses’ Health Study (NHS), NHS II, and Health Professionals Follow-up Study (HPFS). Physical activity was assessed periodically by self-reported questionnaire starting from 1984 in NHS, 1989 in NHSII, and 1986 in HPFS. We used physical activity measured closest before blood collection as exposure. Metabolic profiling was conducted by liquid chromatography-mass spectrometry (LC-MS). Our study included 287 known metabolites, with 64% of them classified as lipids (58 triglycerides [TAGs], 13 diglycerides [DAGs], 13 cholesteryl esters [CEs], 6 lysophosphatidylethanolamines [LPEs], 37 phosphocholines [PCs], 10 lysophosphatidylcholines [LPCs], 24 phosphatidylethanolamines [PEs], and 25 carnitines). We examined associations of physical activity with plasma metabolites using linear regression, and corrected for multiple testing using tail probability of the proportion of false positives (TPPFP) and accounting for correlated tests using bootstrapping. Results: Using linear model adjusting for age, case-control status, labcode, smoking status, fasting status, alcohol intake, and diet quality, physical activity was significantly associated with 27 metabolites after correcting for multiple testing (TPPFP <0.05). Among the 27 identified metabolites, four CEs, eight PCs, and three LPCs were positively associated with physical activity, and five TAGs and four DAGs were inversely associated. After additionally adjusting for body mass index (BMI), the associations of physical activity with the majority of identified metabolites were attenuated; physical activity remained positively associated with three CEs (C18:2, C16:0, and C18:1), three PCs (C36:4 PC-A, C36:0 PC, C34:3 PC plasmalogen), and one LPC (C18:2). Enrichment analysis showed that physical activity was significantly positively associated with the CE category (P value for enrichment=0.048). Conclusions: We identified seven metabolites that were significantly associated with physical activity after adjusting for BMI, which may help identify biomarkers of physical activity and provide insight into biological mechanisms underlying the beneficial effect of being physically active on cardiometabolic health.

By the book: A method for patterning paper with photoresist to create well-defined, millimeter-sized channels comprising hydrophilic paper bounded by hydrophobic polymer is described. This type of patterned paper is a prototype of a class of low-cost, portable, and technically simple platforms for running multiplexed bioassays with microliter volumes of a single biological sample. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z603817_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Soft devices can be bent, stretched, and compressed reversibly, but conventional wires are rigid. This work describes stretchable composites that are easily fabricated with simple tools and commodity materials, and that can provide a strategy for electrical wiring that meets certain needs of soft devices. These composites are made by combining metal wool and elastomeric polymers. Embedding fine (average fiber width ≈25 μm) steel wool (or other metal wools) in a silicone polymer creates an electrically conductive path through the nonconductive elastomer. This composite is flexible, stretchable, compressible, inexpensive, and simple to incorporate into the bodies of soft devices. It is also electrically anisotropic, and shows maximum conductivity along the majority axis of the fibers, but maximum extension perpendicular to this axis. The utility of this composite for creating an electrically conductive path through an elastomer was demonstrated in several devices, including: a soft, solderless breadboard, a soft touch sensor, and a soft strain gauge.

Selenium (Se) is an essential trace element in human nutrition, but its role in certain health conditions, particularly among Se sufficient populations, is controversial. A genome-wide association study (GWAS) of blood Se concentrations previously identified a locus at 5q14 near BHMT. We performed a GW meta-analysis of toenail Se concentrations, which reflect a longer duration of exposure than blood Se concentrations, including 4162 European descendants from four US cohorts. Toenail Se was measured using neutron activation analysis. We identified a GW-significant locus at 5q14 (P < 1 × 10−16), the same locus identified in the published GWAS of blood Se based on independent cohorts. The lead single-nucleotide polymorphism (SNP) explained ∼1% of the variance in toenail Se concentrations. Using GW-summary statistics from both toenail and blood Se, we observed statistical evidence of polygenic overlap (P < 0.001) and meta-analysis of results from studies of either trait (n = 9639) yielded a second GW-significant locus at 21q22.3, harboring CBS (P < 4 × 10−8). Proteins encoded by genes at 5q14 and 21q22.3 function in homocysteine (Hcy) metabolism, and index SNPs for each have previously been associated with betaine and Hcy levels in GWAS. Our findings show evidence of a genetic link between Se and Hcy pathways, both involved in cardiometabolic disease.

Correction for ‘The magnitude of lift forces acting on drops and bubbles in liquids flowing inside microchannels’ by Claudiu A. Stan <italic>et al.</italic>, <italic>Lab Chip</italic>, 2013, <bold>13</bold>, 365–376.

As the most commonly consumed dietary supplement, how multivitamin use associates with risk of mortality remains inconclusive. Methods: We used data from three cohort studies to examine the association of time-varying multivitamin use with risk of mortality. We also emulated a target trial to estimate the association by applying the parametric g-formula. Results: Of 241,068 eligible participants (mean age at baseline: 50 for NHS, 37 for NHSII, and 53 for HPFS), there were 44,415 deaths over 30-years of follow up. Compared to non-users, the pooled age-adjusted harzard ratio (HR) of mortality was 0.92 (95% CI: 0.89, 0.94) and 0.89 (95% CI: 0.88, 0.91) for users who used &lt;1 and ≥1 pill/day, respectively. These results were attenuated after multivariable adjustment (0.97 [0.95, 1.00] and 0.98 [0.96, 0.99], respectively), and the inverse association was primarily due to lower risk of CVD mortality ( table 1 ). In the emulated target trial, the estimated 30-y all-cause mortality under a multivitamin intervention was slightly lower than no intervention ( table 2 ). Conclusions: Multivitamin use may relate to a small reduction in mortality among middle-aged adults.