Suresh Regonda

Ultrasensitive protein detection using lithographically defined Si multi-nanowire field effect transistors.

Low-doped silicon multi-nanowire field effect transistors with high ON/OFF ratio over 10(7) and a low subthreshold swing of 60-120 mV dec(-1) are fabricated using lithographic semiconductor processes. The use of multi-nanowires instead of a single nanowire as sensing elements has shown improved device uniformity and stability in buffer solutions. The device stability is further improved with surface silanization and biasing with a solution gate rather than a backgate. pH sensing with a linear response over a range of 2-9 is achieved using these devices. Selective detection of bovine serum albumin at concentrations as low as 0.1 femtomolar is demonstrated.

Silicon multi-nanochannel FETs to improve device uniformity/stability and femtomolar detection of insulin in serum

Here we demonstrate the use of multiple Si nanochannel (NC) or nanograting (NG) instead of the conventional single nanochannel or nanowire design in biosensors. The NG devices can significantly reduce device-to-device variation, and improve device performance, e.g. higher current, higher ON/OFF ratio, smaller subthreshold slope, lower threshold voltage Vt in buffer solution. NG devices also result in higher sensor stability in buffer and diluted human serum. We believe such improvements are due to reduced discrete dopant fluctuation in the Si nanowires and biochemical noise in the solution because of the multiple-channel design. The improved devices allow us to sense pH linearly with 3-aminopropyltriethoxysilane coated devices, and to selectively detect insulin with limit of detection down to 10 fM in both buffer solution and diluted human serum without pre-purification.

Characterizing nanoimprint profile shape and polymer flow behavior using visible light angular scatterometry

The profile shape and the flow behavior of polymer nanoscale gratings made by a thermal nanoimprint process are precisely examined using visible light angular scatterometry. Nanoimprinted poly(methyl methacrylate) (PMMA) lines with 60–800nm width, 100–200nm height, and varied residual thicknesses of 70–400nm have been investigated using this optical approach, and insightful observations are made regarding residual stress buildup during thermal nanoimprint. In addition, a nonlinear profile model has been developed for scatterometry to monitor the “melting” behavior of PMMA gratings under annealing around its glass transition temperature. The polymer nanostructures were found to relax primarily at high stress regions.

Stability of HSQ nanolines defined by e-beam lithography for Si nanowire field effect transistors

Multiple instability states, e.g., grouped collapse, single collapse, wavy, and grouped wavy states, have been observed in hydrogen silses quioxane (HSQ) nanolines defined by electron beam lithography (EBL). Experimental data show that the critical aspect ratio of the HSQ lines dramatically increase when the line pitch reduced to sub-100-nm, which is opposite to theoretical models for capillary forces and swelling strain. Such contradiction can be well explained only if Young’s modulus is considered as a significantly varying factor. Further, experimental data show a dramatic decrease in swelling strain and increase in oxygen contents in HSQ with increasing EBL dose, indicating that it is the change in Young’s modulus rather than the capillary force or swelling strain that dominates the instability behaviors at the nanoscale. Stable high aspect ratio HSQ nanolines over metal pads were used to make working Si nanowire transistors on Si on insulator substrates. 12–14nm HSQ lines with aspect ratios of 11–14 ...

Simulation of Si nanowire biosensor: Effects of surface and biasing on sensitivity and linearity

We present here a numerically simulated pH sensing performance of Si nanowire (SiNW) FETs. The simulation is formulated based on Fermi-Dirac, Poisson-Boltzman, site-binding and Gouy-Chapman-Stern theories. Device characteristics (Vt, SS, On/Off, etc.) and pH sensing linearity/sensitivity from simulation match well with our sensing experiments using SiNW FETs fabricated with CMOS compatible process. Our study quantitatively shows the biasing under strong inversion yields better linearity, while sub-threshold yields better sensitivity. We also show that high sensitivity and linearity would require oxide surface with high density of reactive groups and good SAMs coverage.

Lithographically Defined Si Nanowire Field Effect Transistors for Biochemical Sensing

A process integration of e-beam lithography, plasma etching, and Si processing have been developed to pattern Si nanowires on crystalline Si on insulator wafers. Si nanowires of 12-50 nm linewidth, 30-70 nm height, and 10 mum length have been made. Using these Si nanowires as conducting channels, field effect transistors using the back Si substrate as gate have been fabricated. Good I-V characteristics have been obtained. With the back-gate configuration, the surface of Si nanowires can be functionalized for biochemical sensing applications.

Sensitive detection of melamine with silicon nanowire field effect transistor biosensor

Melamine, a widely used industry chemical, has been detected in pet foods and some protein-based food commodities, such as milk as a fraudulent substitute for protein since 2007. Melamine with concentrations higher than the safety limits can cause kidney injury. Therefore there is growing needs for a low cost portable sensor that can detect melamine in food. Here, we demonstrate two assay methods of using functionalized Si nanowire transistors (SiNW FETs) to detect melamine with high sensitivity. The direct detection using antibody coated SiNW FETs shows selective detection of melamine down to 50 ppb level (or 2 μM). Another competitive assay takes advantage of competition reaction between the BSASM2-antibody vs. melamine-antibody to indirectly detect the concentration of melamine selectively down to 20 pM level in buffer solutions. The results show that SiNW has the potential to become a portable low cost sensor for melamine detection.

Si multi-nanochannel FETs to improve device uniformity/stability and detection of 10 fM insulin in serum

Here we demonstrate the use of multiple Si nanochannel (NC) or nanograting (NG) instead of the conventional single channel or nanowire design in biosensors can significantly reduce device to device variation, and improve device performance (higher current, higher ON/OFF ratio, smaller SS, lower Vt) in buffer solution. NG devices also result in higher sensor stability (repeated sensing over tens of hours) in buffer and human serum. We believe such improvements are due to reduced discrete dopant fluctuation and biochemical noise in the solution. The improved devices allow us to sense pH linearly with 3-aminopropyltriethoxysilane (APTES) coated devices, and to selectively detect insulin with limit of detection down to 10fM in both buffer solution and human serum without pre-purification.

Ultrasensitive electronic detection of DNA using Si nanograting FETs coated with PNA probes

We report the label-free rapid detection of single stranded DNA segments using lithographic Si nanograting (NG) FET devices coated with single stranded PNA probes. The NGFETs shows improved signal to noise ratio and similar sensitivity in comparison with the single nanowire FETs fabricated on the same chip. The limit of detection of our finFETs reaches sub-femtoMolar. The same devices do not respond significantly to high concentrations of non-complementary DNA segments.

Notice of Retraction Si multi-nanochannel FETs to improve device uniformity/stability and detection of 10 fM insulin in serum

Here we demonstrate the use of multiple Si nanochannel (NC) or nanograting (NG) instead of the conventional single channel or nanowire design in biosensors can significantly reduce device to device variation, and improve device performance (higher current, higher ON/OFF ratio, smaller SS, lower Vt) in buffer solution. NG devices also result in higher sensor stability (repeated sensing over tens of hours) in buffer and human serum. We believe such improvements are due to reduced discrete dopant fluctuation and biochemical noise in the solution. The improved devices allow us to sense pH linearly with 3-aminopropyltriethoxysilane (APTES) coated devices, and to selectively detect insulin with limit of detection down to 10fM in both buffer solution and human serum without pre-purification.