Ruhai Tian

Photoactivation switch from type II to type I reactions by electron-rich micelles for improved photodynamic therapy of cancer cells under hypoxia

Photodynamic therapy (PDT) is an emerging clinical modality for the treatment of a variety of diseases. Most photosensitizers are hydrophobic and poorly soluble in water. Many new nanoplatforms have been successfully established to improve the delivery efficiency of PS drugs. However, few reported studies have investigated how the carrier microenvironment may affect the photophysical properties of photosensitizer (PS) drugs and subsequently, their biological efficacy in killing malignant cells. In this study, we describe the modulation of type I and II photoactivation processes of the photosensitizer, 5,10,15,20-tetrakis(meso-hydroxyphenyl)porphyrin (mTHPP), by the micelle core environment. Electron-rich poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) micelles increased photoactivations from type II to type I mechanisms, which significantly increased the generation of O(2)(-) through the electron transfer pathway over (1)O(2) production through energy transfer process. The PDPA micelles led to enhanced phototoxicity over the electron-deficient poly(D,L-lactide) control in multiple cancer cell lines under argon-saturated conditions. These data suggest that micelle carriers may not only improve the bioavailability of photosensitizer drugs, but also modulate photophysical properties for improved PDT efficacy.

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.

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.

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.

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.

RETRACTED ARTICLE: 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.