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Four types of water-soluble quantum dots (QDs) grafted with different organic coating layers were fabricated, and their sensitivities for hypochlorite/hypochlorous acid (HClO) were examined. It was found that QDs with HClO reactive (methylamino and sulphide groups) coating layers exhibited a protective effect on HClO quenching of QD fluorescence, whereas QDs with hydrocarbon and carboxylate coating layers showed least protection to QD fluorescence quenching by HClO and, thus, has the highest sensitivity for the detection of HClO. The QDs with carboxylate coating layers (QDs-poly-C[O.sub.2.sup.-]) was successfully applied to the quantification of HClO in tap water. The excellent selectivity of the QDs-poly-C[O.sub.2.sup.-] toward hypochlorite against other reactive oxygen species allowed us to monitor myeloperoxidase activity. Finally, the QDs-poly-C[O.sub.2.sup.-] was also used for the detection of hypochlorite in HL60 cells by fluorescent imaging. Hence, QD-poly-C[O.sub.2.sup.-] exhibits great promise as a selective and sensitive HClO probe in chemical and biological systems. 10.1021/ac101929q

The major challenge of prion disease diagnosis at the presymptomatic stage is how to sensitively or selectively discriminate and detect the minute quantity of disease-associated prion protein isoform ([PrP.sup.Res]) in complex biological systems such as serum and brain homogenate. In this contribution, we developed a dual-aptamer strategy by taking the advantages of aptamers, the excellent separation ability of magnetic microparticles (MMPs), and the high fluorescence emission features of quantum dots (QDs). Two aptamers (Apt1 and Apt2), which can recognize their two corresponding distinct epitopes of prion proteins (PrP), were coupled to the surfaces of MMPs and QDs, respectively, to make MMPs-Aptl and QDs-Apt2 ready at first, which then could be coassociated together through the specific recognitions of the two aptamers with their two corresponding distinct epitopes of PrP, forming a sandwich structure of MMPs-Apt1-PrP-Apt2-QDs and displaying the strong fluorescence of QDs. Owing to the different binding affinities of the two aptamers with [PrP.sup.Res] and cellular prion protein ([PrP.sup.C]), both of which have distinct denaturing detergent resistance, our dual-aptamer strategy could be applied to discriminate [PrP.sup.Res] and [PrP.sup.C] successfully in serum. Further identifications showed that the present dual-aptamer assay could be successfully applied to the detection of PrP in 0.01% brain homogenate, about 1000-fold lower than that of commonly applied antibody-mediated assays, which can detect PrP just in 10% brain homogenate, indicating that the present designed dual-aptamer assay is highly sensitive and adequate for clinical diagnosis without isolation of target protein prior to assay. 10.1021/ac101865s

The development of a simple and on-site assay for the detection of organophosphorus pesticed residues is very important for food safety and exosystem protection. This paper reports the surface coordination-originated fluorescence resonance energy transfer (FRET) of CdTe quantum dots (QDs) and a simple ligand-replacement turn-on mechanism for the highly sensitive and selective detection of organophosphorothioate pesticides. It has been demonstrated that coordination of dithizone at the surface of CdTe QDs in basic media can strongly quench the green emission of CdTe QDs by a FRET mechanism. Upon the addition of organophosphorothioate pesticides, the dithizone ligands at the CdTe QD surface are replaced by the hydrolyzate of the organophosphorothioate, and hence the fluorescence is turned on. The fluorescence turn on is immediate, and the limit of detection for chlorpyrifos is as low as ~0.1 nM. Two consecutive linear ranges allow a wide determination of chlorpyrifos concentrations from 0.1 nM to 10 [micro]M. Importantly, the fluorescence turn-on chemosensor can directly detect chlorpyrifos residues in apples at a limit of 5.5 ppb, which is under the maximum residue limit allowed by the U.S. Environmental Protection Agency. The very simple strategy reported here should facilitate the development of fluorescence turn-on chemesensors for chemo/biedetection. 10.1021/ac102531z

An enzyme-linked analytical nanosphere sensor (ANSor) is described, responding to enzyme--substrate turnover in the vicinity of a quantum dot (QD) due to coimmobilized enzyme and pH sensitive ligand. QD capping by mercapto-alkanoic acids were rejected as a pH sensitive ligand, but with the use of a layer-by-layer assembly on mercaptopropionie capped QDs and an intermediate poly(allylamine hydrochloride) layer, anthraquinone sulfonate (calcium red, CaR) was introduced to modify the [pK.sub.a] in the immobilized system > 8. QD--CaR absorption shows spectral overlap with [QD.sub.530] emission at all pHs and gives a complex pH dependent fluorescence resonance energy transfer (FRET) efficiency, due to excited state proton transfer ([[lambda].sub.ex] = 540 nm; [[lambda].sub.em] = 585 nm). In contrast [QD.sub.615]--CaR with spectral overlap between the QD and CaR gave a strong and reproducible pH response. QD--urease and QD--creatinine deiminase conjugates could be linked with pH changes produced by enzyme degradation of urea and creatinine, respectively. Close coupling between the pH sensitive QD and enzyme conjugate maximized signal compared with solution based assays: QD--urease and QD--CD bioconjugates were tested in model biological media (Dulbecco's modified Eagle's Medium and fetal calf serum) and in urine, showing a response in 3-4 min. 10.1021/ac101838n

A highly sensitive competitive immunosensor based on the electrochemiluminescence (ECL) of quantum dots (QDs) was proposed by coupling with an enzymatic amplification. The fabrication process of the immunosensor was traced with atomic force microscopic images and electrochemical impedance spectra. The strong cathodic ECL emission of the immobilized QDs could be detected at a relatively low emission potential. The reduction of dissolved oxygen during the cathodic process provided a self-produced coreactant, [H.sub.2][O.sub.2], for the ECL emission. Using human IgG (HIgG) as a model protein, upon the immuno-recognition of the immobilized HIgG to its antibody labeled simply with horseradish peroxidase, the ECL intensity decreased due to the steric hindrance of the proteins to electron Iransfer. The decrease could be greatly amplified by an enzymatic cycle to consume the self-produced coreactant, leading to a wide calibration range of 0.05 ng [mL.sup.-1] ~ 5 [micro]g [mL.sup.-1] and a low limit of detection for the competitive immunoassay of HIgG. This immunosensor showed good stability and fabrication reproducibility. The immunoassays of practical samples showed acceptable results. This facile immunosensing strategy opened a new avenue for detection of proteins and application of QDs in ECL biosensing. 10.1021/ac1013942

The luminescence of CdSe/ZnS QDs is quenched via electron transfer by hemin/G-quadruplex associated with the particles. This phenomenon is implemented to develop DNA sensors or aptasensers by tailoring hairpin-functionalized QDs that generate the hemin/G-quadruplex quenchers upon sensing of the respective analytes. 10.1021/ac101456x

A versatile immunosensor using a CdTe quantum dots (QDs) coated silica nanosphere (Si/QD) as a label was proposed for ultrasensitive detection of a biomarker. In this approach, silica nanospheres with good monodispersity and uniform structure were employed as the carrier for immobilization of QDs and antibodies. Rabit IgG served as a model protein to demonstrate the performance of the immunosensor. Goat antirabbit IgG antibody was covalently bound to CdTe QDs on the surface of silica nanospheres. CdTe QDs coated with a silica nanosphere label (Si/QD/Ab2) were attached onto the gold electrode surface through a subsequent 'sandwich' immunoreaction. This reaction was confirmed by scanning electron microscopic (SEM) and fluorescence microscopic images. Due to signal amplification from the high loading of CdTe QDs, 6.6- and 5.9-fold enhancements in electrochemiluminescent (ECL) and square-wave voltammetric (SWV) signals for IgG detection were achieved compared to the unamplified method. The detection limits for IgG were 1.3 and 0.6 pg [mL.sup.-l] for ECL and SWV measurements, respectively. The resulting versatile immunosensor possesses high sensitivity, satisfactory reproducibility and regeneration, and good precision. This simple and specific strategy has vast potential to be used in other biological assays. 10.1021/ac100558t

The multicolor and multiplexing capabilities of semiconductor quantum dots (QDs) are most promising for improving the sensitivity and specificity of in vitro molecular and cellular diagnostics. Here, we report the use of multiplexed QDs and wavelength-resolved imaging to detect and characterize a class of low-abundant tumor cells in Hodgkin's lymphoma. Known as the Hodgkin's and Reed-Sternberg (HRS) cells, this class of malignant cells is a pathological hallmark in clinical diagnosis, but it comprises only about 1% of the heterogeneous infiltrating cells in lymph node tissues. To overcome this cellular heterogeneity and rarity problem, we have developed multicolor QD--antibody conjugates to simultaneously detect a panel of four protein biomarkers (CD 15, CD30, CD45, and Pax5) directly on human tissue biopsies. This multiplexing approach allows rapid detection and differentiation of rare HRS cells from infiltrating immune cells such as T and B lymphocytes. We have also carded out clinical translation studies involving six confirmed Hodgkin's lymphoma patients, two suspicious lymphoma cases, and two patients with reactive lymph nodes (but not lymphoma). The results indicate that a distinct QD staining pattern (CD15 positive, CD30 positive, CD45 negative, and Pax5 positive) can be used to not only detect Hodgkin's lymphoma but also differentiate it from benign lymphoid hyperplasia. 10.1021/ac101065b

A novel electrocbemiluminescent (ECL) sensing system was constructed for low-potential detection of metal ion by immobilizing surface-unpassivated CdTe quantum dots (QDs) on a glassy carbon electrode. The surface-unpassivated CdTe QDs were prepared using meso-2,3-dimercaptosuccinic acid (DMSA) as a stabilizer to cap CdTe QDs and characterized with scanning electron micrograph and X-ray photoelectron spectroscopy. The immobilized QDs showed a strong cathodic ECL emission peak at -0.87 V with an onset potential at -0.64 V (vs Ag/AgCl/ saturated KCl) in air-saturated, pH 9.0 HC1--Tris buffer. On the basis of the competition of metal ion to the stabilizer, the quenching effect of metal ion on ECL emission was observed, which led to a sensitive chemical sensing application. Using cupric cation as a model analyte, the sensor showed a linear range from 5.0 nM to 7.0 [micro]M with a detection limit of 3.0 nM and had been successfully applied in the detection of copper in human hair. It could be extended to detect other metal ions with stronger metal--S interaction than with the Cd--S bond. As an example, the sensor could be used to detect [Hg.sup.2+] down to 1.4 nM. The bidentate chelate QD-basod sensor exhibited a promising platform for rapid detection of cations with strong metal--S interaction and could be further applied for development of other low-potential electrochemical sensing systems. 10.1021/ac100315a

A cascade signal amplification strategy was proposed for detection of protein target at ultralow concentration by combining the rolling circle amplification (RCA) technique with oligonucleotide functionalized quantum dots (QDs), multiplex binding of the biotin--strepavidin system, and anodic stripping voltammetric detection. The RCA product containing tandem-repeat sequences could serve as excellent template for periodic assembly of QDs, which presented per protein recognition event to numerous quantum dot tags for electrochemical readout. Both the RCA and the multiplex binding system showed remarkable amplification efficiency, very little nonspecific adsorption, and low background signal. Using human vascular endothelial growth factor as a model protein, the designed strategy could quantitatively detect protein down to 16 molecules in a 100 [micro]L sample with a linear calibration range from 1 aM to 1 pM and was amenable to quantification of protein target in complex biological matrixes. The proposed cascade signal amplification strategy would become a powerful tool for proteomics research and clinical diagnostics. 10.1021/ac100144g

Quantum dot (QD)-induced fluorescence detection of bead-based DNA sandwich hybridization was studied for rapid analysis of the Bacillus spoOA gene in biofilms. Hybridization between two DNA probes and target DNA occurred and the hybridization signal was detected in a flow cytometer. To prepare the bead--DNA capture and QD-DNA detection probes, the coupling or bioconjugation reactions were carefully controlled, it was successfully demonstrated that the fluorescence response of the hybrid complex was linear in the range of 3.2-1000 nM of synthetic target DNA ([R.sup.2] = 0.97) and that the detection limit was 0.02 nM. An optimized labeling method and bead-based DNA hybridization were then applied to real PCR products from a biofilm sample with satisfactory results ([R.sup.2] = 0.94), thereby confirming that the proposed assay provides a rapid, sensitive, and specific method fur Bacillus spoOA gene detection in bofilms. This approach enables multiple target detection using multicolor QD-DNA probes in a shorter time. 10.1021/ac902807n

Owing to their unique optical properties, quantum dots (QDs) with different colors have been applied for simultaneous detection of multiple analytes. However, the use of single QD for multiplex detection of analytes with single-molecule detection has not been explored. Here we report a single QD-based nanosensor for multiplex detection of HIV-1 and HIV-2 at single-molecule level in a homogeneous format. In this single QD-based nanosensor, the QD functions not only as a fluorescence pair for coincidence detection and as a fluorescence-resonance-energy-transfer (FRET) donor for FRET detection but also as a local nanoconcentrator which significantly amplifies the coincidence-related fluorescence signals and the FRET signals. This single-QD-based nanosensor takes advantage of a simple 'mix and detection' assay with extremely low sample consumption, high sensitivity, and short analysis time and has the potential to be applied for rapid point-of-care testing, gene expression studies, high-throughput screening, and clinical diagnostics. 10.1021/ac9026675

A method based on the quenching kinetics for the fluorescence of glutathione capped CdTe quantum dots (GSH-CdTe QDs) was developed for discriminating [Fe.sup.2+] and [Fe.sup.3+], and a GSH-CdTe QDs-Fenton hybrid system was constructed for sensitive and selective determination of trace [Fe.sup.2+]. Although both [Fe.sup.2+] and [Fe.sup.3+] could quench the fluorescence of GSH-CdTe QDs, the quenching kinetics was quite different for [Fe.sup.2+] and [Fe.sup.3+]. The fluorescence of the GSH-CdTe QDs (30 nM) was quenched by about 18% in 1 min after the addition of [Fe.sup.3+] (10 [micro]M), and remained unchanged with further increase of reaction time. In contrast, the fluorescence intensity of the GSH-CdTe QDs decreased by about 65% in the first 5 min after the addition of [Fe.sup.2+] (10 [micro]M), then slowly decreased by 15% in the next 25 minutes. Other transition metal ions like [Cu.sup.2+], [Ni.sup.2+] and [Co.sup.2+], [Zn.sup.2+], and [Mn.sup.2+] also gave very different quenching kinetics of the GSH-CdTe QDs from [Fe.sup.2+]. No significant effect of the capping agents (GSH, thioglycolic acid, and mereaptopropionic acid) for the QDs on the pattern of the time course of the fluorescence of the QDs for [Fe.sup.2+] or [Fe.sup.3+] was observed. To achieve selective determination of [Fe.sup.2+] in the presence of [Fe.sup.3+], trace [H.sub.2][O.sub.2] was introduced to establish a QDs-Fenton hybrid system. The Fenton reaction between [Fe.sup.2+] and [H.sub.2][O.sub.2] resulted in hydroxyl radicals which can effectively quench the fluorescence of the QDs through electron transfer from the conduction band of the QDs to the single occupied molecular orbit of hydroxyl radicals. The high redox potential of hydroxyl radicals (2.8 V) permits more effective quenching of the fluorescence of the QDs than [Fe.sup.2+]. The detection limit of the developed method was 5 nM for [Fe.sup.2+]. The recovery of [Fe.sup.2+] spiked in water samples ranged from 90% to 105%.

Herein, a sensitive and selective sensor for biothiols based on the recovered fluorescence of the CdTe quantum dots (QDs)-Hg(II) system is reported. Fluorescence of QDs could be quenched greatly by Hg(II). In the presence of biothiols, such as glutathione (GSH), homocysteine (Hcy), and cysteine (Cys), however, Hg(II) preferred to react with them to form the Hg(II)--S bond because of the strong affinity with the thiols of biothiols rather than quenching the fluorescence of the QDs. Thus, the fluorescence of CdTe QDs was recovered. The restoration ability followed the order GSH > Hcy > Cys due to the decreased steric hindrance effect. A good linear relationship was obtained from 0.6 to 20.0 [micro]mol [L.sup.-1] for GSH and from 2.0 to 20.0 [micro]mol [L.sup.-1] for Cys, respectively. The detection limits of GSH and Cys were 0.1 and 0.6 [micro]mol [L.sup.-1], respectively. In addition, the method showed a high selectivity for Cys among the other 19 amino acids. Furthermore, it succeeded in detecting biothiols in the Hela cell.

The important roles of biothiols in biological systems have attracted great interest in the determination of biothiols. Although great progress has been made in fluorescent biothiol probes, near-infrared (NIR) fluorescent probes for biothiols are rather few even such NIR probes can avoid interference from biological media such as tissue autofluorescence and scattering light, and thereby facilitate relatively interference-free sensing. Herein, we report photoactivated CdTe/CdSe quantum dots (QDs) as a novel NIR fluorescent probe for biothiols. The photoactivated CdTe/CdSe QDs based NIR fluorescent probe offers good sensitivity and selectivity for detecting cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) in the presence of 20 other amino acids, main relevant metal ions, and some other molecules in biological fluids. The recovery of spiked 5.0 [micro]M thiols in human urine, plasma, and cell extracts ranges from 90% to 109%. The precision for nine replicate measurements of the thiols at 5.0 [micro]M is in the range from 1.6% to 1.8%. The detection limits for Cys, Hcy, and GSH are 131, 26, and 20 nM, respectively. This assay is based on both the superior photoactivity of CdTe/ CdSe QDs and the strong affinity of thiols to photoactivated CdTe/CdSe QDs. The addition of thiols into the photoactivated CdTe/CdSe Q Ds improves the passivation of the illumination-induced traps, meanwhile reduces most of Se(IV) and Te(IV) on the surface of photoactivated CdTe/CdSe QDs so as to improve the fluorescence property.

Solid-phase assays using immobilized quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) have been developed for the selective detection of nucleic acids. QDs were immobilized on optical fibers and conjugated with probe oligonucleotides. Hybridization with acceptor labeled target oligonucleotides generated FRET-sensitized acceptor fluorescence that was used as the analytical signal. A sandwich assay was also introduced and avoided the need for target labeling. Green and red emitting CdSe/ZnS QDs were used as donors with Cy3 and Alexa Fluor 647 acceptors, respectively. Quantitative measurements were made via spectrofluorimetry or fluorescence microscopy. Detection limits as low as 1 nM were obtained, and the discrimination of single nucleotide polymorphisms (SNPs) with contrast ratios as high as 31:1 was possible. The assays retained their selectivity and at least 50% of their signal when tested in bovine serum and against a large background of noncomplementary genomic DNA. Mixed films of the two colors of QD and two probe oligonucleotide sequences were prepared for multiplexed solid-phase hybridization assays. It was possible to simultaneously detect two target sequences with retention of selectivity, including SNP discrimination. This research provides an important precedent and framework for the future development of QD-based bioassays and biosensors.

We have developed a new fluorescent ensemble probe comprising an ionic conjugate between water-soluble thioglycolic acid (TGA) capped CdTe quantum dots (QDs) and [Ru(bpy).sub.2][(dppx).sup.2+] for the dual-color detection of complementary double-stranded DNAs (dsDNA). To provide the platform for DNA detection, the Rucomplex was first employed as an effective fluorescence quencher to TGA capped QDs via photoinduced electron transfer process. Because of its strong binding affinity with [Ru(bpy).sub.2][(dppx).sup.2+], complementary dsDNA can break up the low fluoresced ionic ensemble, set free the luminescent QDs, and concomitantly generate the [Ru(bpy).sub.2][(dppx).sup.2+] intercalated DNA complex. Thus, the recognition of dsDNA by [Ru(bpy).sub.2][(dppx).sup.2+] can be realized via both the restoration of QDs fluorescence and the emergence of a new fluorescence emission signal of the quencher--substrate at 609 nm, while single-stranded DNA, ribonucleic acid, bovine albumin serum, and biological relevant metal ions cannot produce the similar results. Therefore, a simple, fast, sensitive, and highly selective assay for dsDNA has been realized.

Recent advances in single-molecule detection, nanotechnology, and aptameric sensors hold exciting promise for many potential applications. By functionalizing the surface of a quantum dot (QD) with aptamers which can recognize cocaine, and taking advantage of single-molecule detection and fluorescence resonance energy transfer (FRET) between 605QD and Cy5 and Iowa Black RQ, we develop a single-QD-based aptameric sensor that is capable of sensing the presence of cocaine through both signal-off and signal-on modes. In comparison with the established aptameric sensors, this single-QD-based aptameric sensor has the significant advantages of simple sample preparation, high sensitivity, and extremely low sample consumption. With the advances in the development of varieties of aptamers for small molecules, nucleic acids, metal ions, and proteins, this single-QD-based aptameric sensor might find wide application in forensic analysis, environmental monitoring, and clinic diagnostics.

A sensing system based on the photoinduced electron transfer of quantum dots (QDs) was designed to measure the interaction of anticancer drug and DNA, taking mitoxantrone (MTX) as a model drug. MTX adsorbed on the surface of QDs can quench the photoluminescence (PL) of QDs through the photoinduced electron-transfer process; and then the addition of DNA will bring the restoration of QDs PL intensity, as DNA can bind with MTX and remove it from QDs. Sensitive detection of MTX with the detection limit of 10 nmol [L.sup.-1] and a linear detection range from 10 nmol [L.sup.-1] to 4.5 [micro]mol [L.sup.-1] was achieved. The dependence of PL intensity on DNA amount was successfully utilized to investigate the interactions between MTX and DNA. Both the binding constants and the sizes of binding site of MTX-DNA interactions were calculated based on the equations deduced for the PL recovery process. The binding constant obtained in our experiment was generally consistent with previous reports. The sensitive and speedy detection of MTX as well as the avoidance of modification or immobilization process made this system suitable and promising in the drug-DNA interaction studies.

Zinc sulfide (ZnS) semiconductor nanoparticles (NPs) capped with a variety of functional groups including bare ZnS NPs, 3-mercaptopropanoic acid (ZnS-3-MPA), sodium citrate (ZnS-citrate), cysteamine (ZnS-Cys), and 2-mercaptoethane sulfonate (ZnS-2-MES) have been investigated as the matrix and affinity probes for analysis of [alpha]-, [beta]-, and [gamma]-cyclodextrins (CDs), ubiquitin, and insulin in biological samples by using surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS). Various parameters that would influence the ionization efficiency and sensitivity of these ZnS NPs in SALDI-TOF-MS were examined including the effect of capping agents, sample pH, ion abundance, and concentration of ZnS NPs. Among these ZnS NPs, our results have demonstrated that ZnS-3-MPA exhibited the highest efficiency toward CDs, ubiquitin, and insulin for high-sensitivity detection in SALDI-TOF-MS. The detection limits were 20-55 nM for CDs, 91 nM for ubiquitin, and 85 nM for insulin. The applicability of the present method is demonstrated by detection of ubiquitin-like proteins in oyster mushroom and also in the analysis of analytes in biological samples such as human urine and plasma. To our best knowledge, this is the first time semiconductor NPs were used as the matrix and affinity probes for high-sensitivity detection of organic and biomolecules in SALDI-TOF-MS. This approach exhibits the advantages of being simple, rapid, efficient, and straightforward for direct analysis of organic and biological samples in SALDI-TOF-MS without the need for time-consuming separation processes, tedious washing steps, or further laborious purification. In addition, it also can provide a sensitive and reliable quantitative assay for small- and large-molecule analysis with the detectable mass up to 8500 Da. We believe that this novel ZnS nanoprobe is simple, efficient, lower cost (compared with Au, Ag, and Pt NPs), fast, and with the potential for high-throughput analysis in SALDI-TOF-MS.

Rapid and sensitive assay of proteases and their inhibition in a high-throughput manner is of great significance in the diagnostic and pharmaceutical fields. We developed a multiplexed assay system of proteases and their inhibition by measuring the energy transfer between quantum dots (QDs) and gold nanoparticles (AuNPs) on a glass slide. In this system, while the photoluminescence (PL) of donor QDs immobilized on a surface was quenched due to the presence of AuNPs (energy acceptor) in close proximity, the protease activity caused modulation in the efficiency of the energy transfer between the acceptor and donor, thus enabling the protease assay. In comparison to the QD-dye system, the conjugate of the QD-AuNP gave rise to higher energy transfer efficiency, resulting in quantitative assay of proteases with more sensitivity. When matrix metalloproteinase, caspase, and thrombin were tested, a multiplexed assay was successfully achieved since the AuNP could be used as a common energy acceptor in conjunction with QDs having different colors. Our system is anticipated to find applications in the diagnosis of protease-related diseases and screening of potential drugs with high sensitivity in a high-throughput way.

A novel method for the fast identification of genetic material utilizing a micro-DNA amplification and analysis device ([micro]-DAAD) consisting of multiple PCR microreactors with integrated DNA microarrays was developed. The device was fabricated in Si-technology and used for the genotyping of Chinese medicinal plants on the basis of differences in the noncoding region of the 5S-rRNA gene. Successful amplification of the genetic material and the consecutive analysis of the fluorescent-labeled amplicons in the [micro]-DAAD by the integrated oligonucleotide probes were demonstrated. Parallel analysis was performed by loading the four PCR reactors of the [micro]-DAAD with different samples of 3-[micro]L volume. Temperature sensors and heating elements of the [micro]-DAAD enable precise temperature control and fast cycling, allowing the rapid completion of a combined amplification and analysis (hybridization) experiment.

Silicon microchips with immobilized antibodies were used to develop microfluidic enzyme immunoassays using chemiluminescence detection and horseradish peroxidase (HRP) as the enzyme label. Polyclonal anti-atrazine antibodies were coupled to the silicon microchip surface with an overall dimension of 13.1 x 3.2 mm, comprising 42 porous flow channels of 235-[micro]m depth and 25-[micro]m width. Different immobilization protocols based on covalent or noncovalent modification of the silica surface with 3-aminopropyltriethoxysilane (APTES) or 3-glycidoxypropyltrimethoxysilane (GOPS), linear polyethylenimine (LPEI, MW 750 000), or branched polyethylenimine (BPEI, MW 25 000), followed by adsorption or covalent attachment of the antibody, were evaluated to reach the best reusability, stability, and sensitivity of the microfluidic enzyme immunoassay ([mu]FEIA). Adsorption of antibodies on a LPEI-modified silica surface and covalent attachment to physically adsorbed BPEI lead to unstable antibody coatings. Covalent coupling of antibodies via glutaraldehyde (GA) to three different functionalized silica surfaces (APTES--GA, LPEI--GA, and GOPS-BPEI--GA) resulted in antibody coatings that could be completely regenerated using 0.4 M glycine/HCl, pH 2.2. The buffer composition was shown to have a dramatic effect on the assay stability, where the commonly used phosphate buffer saline was proved to be the least suitable choice. The best long-term stability was obtained for the LPEI--GA surface with no loss of antibody activity during one month. The detection limits in the [micro]FEIA for the three different immuno surfaces were 45, 3.8, and 0.80 ng/L (209, 17.7, and 3.7 pM) for APTES--GA, LPEI--GA, and GOPS--BPEI--GA, respectively.

Single-crystal semiconductors used as chemical sensors possess chemical, electrical, and optical coupling properties to serve as binding platforms for gaseous and solution analytes. This review discusses characterization of adsorbate-coated semiconductor surfaces and their influence on the semiconductor's physicochemical and electrical properties leading to the final signal transduction.

A comparison of the stability and sensitivity for two different sensor types (semiconductor Sn[O.sub.2] devices, amperometric electrochemical sensors) has been performed. Sensitivities and drifts in the signal and in the background for various concentrations of CO have been studied for thick-film Sn[O.sub.2] sensors (Pt and Pd doped) for a period in excess of 8 months. Similar performance data have been recorded for commercial amperometric sensors for a period in excess of 4 years. The two different sensor types investigated here were also compared to the well-known commercial Figaro TGS 822 sensor at similar concentrations. An objective approach for comparing different types of sensors has been developed using the 'analytical sensitivity'.

The photoelectrochemical process, semiconductor-electrolyte interface (SEI), provides an improved method of measuring electron-transfer (ET) reactions. SEI processes exhibit variations depending on the type of semiconductor electrode and redox electrolyte employed. The electrode materialsused are composed of single crystals, polycrystalline thin films, macroscopic titanium dioxide and quantized-layers, while electrolyte redox solutions involve polymer films, diffusive, adsorbed and immobilized systems. Furthermore, monitoring the duration of photogenerated reactants determines interfacial ET reaction rates.

The wide range of prospective technological applications in electronics, optics, biomedicine, mechanics, and integrated nanostructures are of great interest. The two fundamental steps in nanotechnological processes include, control of nanocrystal structures, and arrangement of nanostructures within the building blocks of special nanodevices.

The development of a novel chip-based multianalyte detection system with a cardiac theme is reported. This work follows the initial reports of 'electronic taste chips' whereby multiple solution-phase analytes such as acids, bases, metal cations, and biological cofactors were detected and quantitated. The newly fashioned 'cardiac chip' exploits a geometry that allows for isolation and entrapment of single polymeric spheres in micromachined pits while providing to each bead the rapid introduction of a series of reagents/washes through microfluidic structures. The combination of these miniaturized components fosters the completion of complex assays with short analysis times using small sample volumes. Optical signals derived from single beads are used to complete immunological tests that yield outstanding assay characteristics. The power and utility of this new methodology is demonstrated here for the simultaneous detection of the cardiac risk factors, C-reactive protein and interleukin-6, in human serum samples. This demonstration represents the first important step toward the development of a useful cardiac chip that targets numerous risk factors concurrently and one that can be customized readily for specific clinical settings.

The first discotic system with an unusual self-organization behavior over long-range to form spherulite textures is reported. Because of its processability and modulated, self-organization behavior, the system is a promising candidate as an active component of electronic devices.

A simple method 'hot lift off' procedure is introduced for creating micropatterns in organic semiconductor microcystalline films, which is used to fabricate organic field effect transisters (OFETs). This is an attractive alternative approach for conventional organic semiconductor microsrystalline patterning technique.