Jianmin Wu

Image‐Contrast Technology Based on the Electrochemiluminescence of Porous Silicon and Its Application in Fingerprint Visualization

The electrochemiluminescence (ECL) of porous silicon (pSi) has attracted great interest for its potential application in display technology and chemical sensors. In this study, we found that pSi with a different surface chemistry displayed an apparently different dynamic ECL process. An image-contrast technology was established on the basis of the intrinsic mechanism of the ECL dynamic process. As a proof of principle, the visualization of latent fingerprints (LFPs) and in situ detection of TNT in fingerprints was demonstrated by using the ECL-based image-contrast technology.

Optical ammonia gas sensor based on a porous silicon rugate filter coated with polymer-supported dye.

An ammonia gas sensor chip was prepared by coating an electrochemically-etched porous Si rugate filter with a chitosan film that is crosslinked by glycidoxypropyltrimethoxysilane (GPTMS). The bromothylmol blue (BTB), a pH indicator, was loaded in the film as ammonia-sensing molecules. White light reflected from the porous Si has a narrow bandwidth spectrum with a peak at 610 nm. Monitoring reflective optical intensity at the peak position allows for direct, real-time observation of changes in the concentration of ammonia gas in air samples. The reflective optical intensity decreased linearly with increasing concentrations of ammonia gas over the range of 0-100 ppm. The lowest detection limit was 0.5 ppm for ammonia gas. At optimum conditions, the full response time of the ammonia gas sensor was less than 15s. The sensor chip also exhibited a good long-term stability over 1 year. Therefore, the simple sensor design has potential application in miniaturized optical measurement for online ammonia gas detection.

Metal ion mediated molecularly imprinted polymer for selective capturing antibiotics containing beta-diketone structure.

A new molecularly imprinted polymer (MIP) targeting to quinolones (Qs) and tetracyclines (TCs) was synthesized using itaconic acid (ITA) and ciprofloxacin (CIP) as a functional monomer and template molecule, respectively. Factors affecting the overall performance of MIP were investigated, and the results showed that Fe(3+) ion play a vital role in the formation of MIP with high molecular imprinting effect. Meanwhile, the chelating ability of monomer, species of template molecule, as well as the molar ratio of monomer and template also contribute to the performance of the obtained MIP. Cyclic voltammetry verified that, with the participation of Fe(3+) ions, a ternary complex of ITA-Fe(3+)-CIP could be formed before polymerization. Compared with conventional MIP prepared from commonly used monomer, methacrylic acid (MAA), the new MIP show significantly enhanced molecular imprinting effect and higher capacity for specific adsorption of target compounds as revealed by static and dynamic binding experiments. The MIP was successfully used as solid-phase extraction (SPE) adsorbent for enriching a broad spectrum of antibiotics containing beta-diketone structure from surface water sample. HPLC detection showed that high recovery rate (78.6-113.6%) was found in these spiked antibiotics, whereas recovery rate for the non structurally related drugs, epinephrine (EP) and dopamine (DOPA), was very low (4.7-7.6%) on the MIP cartridges. The results demonstrate that the MIP prepared by the strategy proposed in this work, could specifically target to a series of structurally related antibiotics containing beta-diketone structure.

A label-free optical sensor based on nanoporous gold arrays for the detection of oligodeoxynucleotides

Interest in using nanoporous materials for sensing applications has increased. The present study reports a method of preparing well-ordered nanoporous gold arrays using a porous silicon (PSi) template. Gold nanolayer could be electrodeposited on the surface of the PSi template at low electrolysis currents in low concentration of chloroauric acid (HAuCl(4)) solution. Surface morphology characterizations and optical measurements revealed that a PSi-templated nanoporous gold (Au-PSi) array well replicated the nanoporous structure and retained the optical properties of PSi. Fourier transform reflectometric interference spectra showed that a characteristic blue-shifted effective optical thickness (EOT) was observed due to the low refractive index of the gold film. An optical DNA biosensor was then fabricated via the self-assembly of single-stranded DNA (ssDNA) with a specific sequence on the surface of Au-PSi. The attachment of ssDNA and its hybridization with target oligonucleotides (ODNs) persistently caused the blue shift of the EOT. Consequently, a relationship between the EOT shift and the ODN concentration was established. The mechanism of the optical response caused by DNA hybridization on the Au-PSi surface was qualitatively explained by the electromagnetic theory and electrochemical impedance spectroscopy (EIS). The lowest detection limit for target ODNs was estimated at around 10(-14) mol L(-1), when the baseline noise, a variation in the value of EOT is around 5 nm. The fabricated Au-PSi based optical biosensor has potential use in the discovery of new ODN drugs because it will be able to detect the binding event between ODNs and the target DNA.

FTRIFS biosensor based on double layer porous silicon as a LC detector for target molecule screening from complex samples

Post-column identification of target compounds in complex samples is one of the major tasks in drug screening and discovery. In this work, we demonstrated that double layer porous silicon (PSi) attached with affinity ligand could serve as a sensing element for post-column detection of target molecule by Fourier transformed reflectometric interference spectroscopy (FTRIFS), in which trypsin and its inhibitor were used as the model probe-target system. The double layer porous silicon was prepared by electrical etching with a current density of 500 mA/cm(2), followed by 167 mA/cm(2). Optical measurements indicated that trypsin could infiltrate into the outer porous layer (porosity 83.6%), but was excluded by the bottom layer (porosity 52%). The outer layer, attached with trypsin by standard amino-silane and glutaraldehyde chemistry, could specifically bind with the trypsin inhibitor, acting as a sample channel, while the bottom layer served as a reference signal channel. The binding event between the attached trypsin and trypsin inhibitor samples could be detected by FTRIFS in real-time through monitoring the optical thickness change of the porous silicon layer. The baseline drift caused by sample matrix variation could be effectively eliminated by a signal correction method. Optical signals had a linear relationship with the concentration of trypsin inhibitor in the range of 10-200 ng mL(-1). The FTRIFS biosensor based on double layer porous silicon could be combined with a UV detector for screening the target molecule from complex component mixtures separated by a LC column. Using an LC-UV-FTRIFS system, a fraction containing a trypsin inhibitor could be separated from a soybean extract sample and identified in real-time.

Use of a porous silicon–gold plasmonic nanostructure to enhance serum peptide signals in MALDI-TOF analysis

Small peptides in serum are potential biomarkers for the diagnosis of cancer and other diseases. The identification of peptide biomarkers in human plasma/serum has become an area of high interest in medical research. However, the direct analysis of peptides in serum samples using mass spectrometry is challenging due to the low concentration of peptides and the high abundance of high-molecular-weight proteins in serum, the latter of which causes severe signal suppression. Herein, we reported that porous semiconductor-noble metal hybrid nanostructures can both eliminate the interference from large proteins in serum samples and significantly enhance the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) yields of peptides captured on the nanostructure. Serum peptide fingerprints with high fidelity can be acquired rapidly, and successful discrimination of colorectal cancer patients based on peptide fingerprints is demonstrated.

Capture, Enrichment, and Mass Spectrometric Detection of Low-Molecular-Weight Biomarkers with Nanoporous Silicon Microparticles

Mining the disease information contained in the low-molecular-weight range of a proteomic profile is becoming of increasing interest in cancer research. This work evaluates the ability of nanoporous silicon microparticles (NPSMPs) to capture, enrich, protect, and detect low-molecular-weight peptides (LMWPs) sieved from a pool of highly abundant plasma proteins. The average pore size and porosity of NPSMPs are controlled by the electrochemical preparation conditions, and the critical parameters for admission or exclusion of protein with a definite molecular weight are determined by reflectometric-interference Fourier transform spectroscopy (RIFTS). Sodium dodecyl sulfate polyacrylamide-gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) analysis of the proteins captured by the NPSMPs show that the chemical nature of the NPSMPs surface and the solution pH also play vital roles in determining the affinity of NPSMPs for target analytes. It is found that carboxyl-terminated porous microparticles with a porosity of 26% (pore diameter around 9.0 nm) specifically fractionate, enrich and protect LMWPs sieved from either simulated samples or human serum samples. Moreover, NPSMPs containing captured peptides can be directly spotted onto a MALDI plate. When placed in a conventional MALDI matrix, laser irradiation of the particles results in the release of the target peptides confined in the nanopores, which are then ionized and detected in the MALDI experiment. As a proof-of-principle test case, mass spectra of NPSMPs prepared using serum from colorectal cancer patients and from control patients can be clearly distinguished by statistical analysis. The work demonstrates the utility of the method for discovery of biomarkers in the untapped LMWP fraction of human serum, which can be of significant value in the early diagnosis and management of diseases.

An Optical Olfactory Sensor Based on Porous Silicon Infiltrated with Room‐Temperature Ionic Liquid Arrays

Chemical and biological optical sensors based on porous silicon (PSi) have been intensively studied due to their large specific surface area, tunable pore structure, and a variety of transduction mechanisms. The sorption of the target molecules into the silicon pores alters the refractive index and, consequently, optical properties of PSi. Optical sensors based on PSi Fabry–P rot thin layers, waveguides, Bragg mirrors, luminescent and reflective microcavities (MCs) have been reported. Of these, PSi rugate filters are promising materials for the fabrication of gas sensors, in which two mechanisms are usually involved. Condensable vapors can be detected by PSi due to their tendency to condense into nanometer-sized pores by microcapillary action at temperatures well above the dew point of the liquid.As a result, the void space in the porous structure is filled with condensed vapor, leading to an increase of the average refractive index of the porous film. Gas can be also detected by specific adsorption onto the pore wall of the PSi through physical or chemical adsorptive processes. However, most of the gas sensors based on PSi materials demonstrate low specificity towards target molecules, since most of the condensation or adsorption processes involved in PSi-based sensors are nonselective. To resolve this problem, the surface of PSi has to be functionalized with specific chemical species that should exhibit strong affinity to target analytes. For example, conjugated polymers entrapped in PSi microcavities have been studied as optical sensors to selectively detect low-volatile explosives, such as trinitrotoluene. However, the diffusion rate of target molecules in polymers is slow, displaying a low-responding speed and poor reversibility. In principle, sensing material with a low glass temperature (Tg) is highly recommended. Liquids could be attractive sensing materials because partition and diffusion of molecules in liquids is relatively fast, although evaporation is another problem when using liquids. Recently, ionic liquids (ILs) have been used as sensing materials for quartz crystal microbalance (QCM)-based vapor-sensing devices. ILs have negligible vapor pressure and high thermal stability in air. These unique properties make them well-suited for acting as promising sensing elements for the detection of volatile organic compounds (VOCs). ILs are excellent solvents that can exploit many types of solvent–solute interactions, including hydrogen bonding, p–p interactions, dipolar interactions, and ionic interactions. In an individual IL–analyte system, different interactions might occur simultaneously. More importantly, the synthetic flexibility allows the tailoring of ILs with a broad range of chemical structures. Accordingly, the interaction of the target analyte with an array of ILs with different chemical structure will result in a unique partition profile. ILs usually consist of cations and anions, with each ion providing a different, completely independent, function. The tremendous structural and chemical diversity of ILs, as well as their remarkable thermal stability, offer an opportunity to design a cross-reactive sensor array. Detection and classification of gaseous analytes with pattern recognition at room temperature can thus be achieved. Herein, we report for the first time an IL array-patterned PSi rugate filter sensor (PSi/ILs) for optical detection and recognition of VOCs. Compared with QCM-based transducers, the optical transducers are more compatible with image technologies, which facilitate the rapid acquisition of data from a sensor array. The procedure for the preparation of an IL array-modified PSi is depicted in Scheme 1. As shown in the scheme,

Bacteria detection based on its blockage effect on silicon nanopore array.

Bacteria detection plays an important role in the guarantee of food and water safety. This work proposed a new sensing strategy for the rapid detection of bacteria based on its blockage effect on nanopore array, which was prepared from electrochemically etched silicon. With the assistance of microfluidic technology, the nanopore array attached with Escherichia coli antibody can selectively and rapidly capture E. coli bacteria, resulting in the decrease of pore accessibility. The signal of pore blockage can be measured by in-direct Fourier Transformed Reflectometric Interference Spectroscopy (FT-RIS). The pore blockage signal has a linear relationship with the logarithm of bacterial density in aqueous sample within the range from 10(3) to 10(7)cfuml(-1). Due to the specific interaction between the antibody and target bacteria, only the E. coli sample displayed significant pore blockage effect, whereas the non-target bacteria, Nox and P17, almost did not show any pore blockage effect. The strategy established in this work might be pervasively applied in the rapid detection of target bacteria and cell in a label-free manner.

Nanoporous Gold Channel with Attached DNA Nanolock for Drug Screening

Soft matter, which is sensitive to weak interaction and easily deformed by external stimuli, plays essential roles in natural sensing systems. For example, the allosteric effect of protein in ion channels dominates the selective ion transportation in cellular processes. [ 1 ] Inspired by natural systems, a wide variety of artifi cial sensing systems have been constructed from soft matter. Recently, synthetic nanosensors comprising soft matter and solid-state nanomaterials have shown excellent advantages for their high sensitivity, as well as a wide variety of signal transducing mechanisms. [ 2 ] Soft matter used in nanosensor systems usually includes polymer, [ 3 ] hydrogel, [ 4 ]