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The research areas of tissue engineering and drug development have displayed increased interest in organ-on-a-chip studies, in which physiologically or pathologically relevant tissues can be engineered to test pharmaceutical candidates. Microfluidic technologies enable the control of the cellular microenvironment for these applications through the topography, size, and elastic properties of the microscale cell culture environment, while delivering nutrients and chemical cues to the cells through continuous media perfusion. Traditional materials used in the fabrication of microfluidic devices, such as poly(dimethylsiloxane) (PDMS), offer high fidelity and high feature resolution, but do not facilitate cell attachment. To overcome this challenge, we have developed a method for coating microfluidic channels inside a closed PDMS device with a cell-compatible hydrogel layer. We have synthesized photocrosslinkable gelatin and tropoelastin-based hydrogel solutions that were used to coat the surfaces under continuous flow inside 50 μm wide, straight microfluidic channels to generate a hydrogel layer on the channel walls. Our observation of primary cardiomyocytes seeded on these hydrogel layers showed preferred attachment as well as higher spontaneous beating rates on tropoelastin coatings compared to gelatin. In addition, cellular attachment, alignment and beating were stronger on 5% (w/v) than on 10% (w/v) hydrogel-coated channels. Our results demonstrate that cardiomyocytes respond favorably to the elastic, soft tropoelastin culture substrates, indicating that tropoelastin-based hydrogels may be a suitable coating choice for some organ-on-a-chip applications. We anticipate that the proposed hydrogel coating method and tropoelastin as a cell culture substrate may be useful for the generation of elastic tissues, e.g. blood vessels, using microfluidic approaches.

A small synthetic peptide with nanomolar affinity for cardiac troponin I (TnI), previously identified from a polyvalent phage displayed library, has been immobilized on a gold surface for TnI detection. The binding affinity of gold-immobilized peptides for TnI was studied and compared with that of phage-immobilized peptides. Quartz crystal microbalance (QCM), cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) were used to monitor both the immobilization and target binding processes. All three techniques show that the binding is specific for TnI as compared to a streptavidin (SA) control. The response curves obtained at TnI concentrations ranging from 0 to 10 [micro]g/mL, using both QCM and EIS, were also compared. For the EIS measurements, the sensitivity was 0.30 [+ or -] 0.030 normalized impedance/ ([micro]g/ mL) and the limit of detection (LOD) was 0.34 [micro]g/mL Using the QCM, a sensitivity of 18 [+ or -] 1 Hz/([micro]g/mL) was obtained, corresponding to an LOD of 0.11 [micro]g/mL Although the QCM demonstrated a lower LOD as compared to EIS, the latter technique exhibited a larger linear dynamic range than QCM. In a relevant tissue culture milieu, Minimum Essential Media (MEM), the sensitivity of the EIS measurement was greater than that obtained in a phosphate buffer system (PBS). The kinetics of target binding using QCM were analyzed by two independent methods, and the dissociation constants ([K.sub.D]) = 66 [+ or -] 4 nM and 17 [+ or -] 8 nM) were an order of magnitude higher than that calculated for the polyvalent phage particles ([K.sub.D]) = 2.5 [+ or -] 0.1 nM). Even though the affinity of the immobilized peptides for TnI was somewhat reduced, overall, these results demonstrate that peptides obtained from the biopanning of phage display libraries can be readily used as sensing probes in biosensor development. 10.1021/ac101657h

A microchip capillary electrophoresis (MCE) system has been developed for the determination of perchlorate in drinking water. The United States Environmental Protection Agency (USEPA) recently proposed a health advisory limit for perchlorate in drinking water of 15 parts per billion (ppb), a level requiring large, sophisticated instrumentation, such as ion chromatography coupled with mass spectrometry (IC-MS), for detection. An inexpensive, portable system is desired for routine online monitoring applications of perchlorate in drinking water. Here, we present an MCE method using contact conductivity detection for perchlorate determination. The method has several advantages, including reduced analysis times relative to IC, inherent portability, high selectivity, and minimal sample pretreatment. Resolution of perchlorate from more abundant ions was achieved using zwitterionic, sulfobetaine surfactants, N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate (HDAPS) and N-tetradecylN,N-dimethyl-3-ammonio-1-propane sulfonate (TDAPS). The system performance and the optimization of the separation chemistry, including the use of these surfactants to resolve perchlorate from other anions, are discussed in this work. The system is capable of detection limits of 3.4 [+ or -] 1.8 ppb (n = 6) in standards and 5.6 [+ or -] 1.7 ppb (n = 6) in drinking water. 10.1021/ac9029086

The superoxide radical anion (SO) is a critical biomarker for monitoring cellular stress responses. Electrochemical SO biosensors are frequently constructed through the covalent immobilization of cytochrome c (Cyt c) onto self-assembled monolayers (SAMs); however, a detailed comparison of these systems as well as configuration influence on SO detection is needed to enable robust applications. Two reaction pathways, oxidation of SO by the SAM-modified gold electrode or electron transfer through a protein and monolayer relay, may be involved during the electrochemical detection of SO with Cyt c, depending on the SAM that is used. Although electrodes with SAMs alone can exhibit a high sensitivity and low limit of detection (LOD) for the SO, they can suffer from a strong response to the presence of interferents such as hydrogen peroxide and ascorbic acid. Electrodes with immobilized Cyt c show decreased sensitivity, but exhibit better selectivity and resistance to fouling in complex media. Considering the trade-offs between sensitivity, selectivity, and LOD for SO detection, a bioelectrode made with Cyt c immobilized on dithiobis(succinimidyl)propionate (DTSP) appears to be the most suitable configuration. In phosphate buffer, the DTSP/Cyt c electrode has a sensitivity of 410 nA [micro][M.sup.-1] [cm.sup.-2] and an LOD for SO of 73 nM. Results are also presented for the detection of SO in a complex tissue culture media (MEM) with and without serum, and the sensitivity of the DTSP/Cyt c in MEM in the absence of serum increased to 640 nA [micro][M.sup.-1] [cm.sup.-2]. By measuring SO with a DTSP/Cyt c electrode before and after the addition of a bolus of the superoxide dismutase (SOD) enzyme, the specificity of the SOD enzyme can be combined with the sensitivity of Cyt c system.

Here, we report a catalytic beacon sensor for uranyl (U[O.sup.2+.sub.2]) based on an in vitro-selected U[O.sup.2+.sub.2]-specific DNAzyme. The sensor consists of a DNA enzyme strand with a 3' quencher and a DNA substrate with a ribonucleotide adenosine (rA) in the middle and a fluorophore and a quencher at the 5' and 3' ends, respectively. The presence of U[O.sup.2+.sub.2] causes catalytic cleavage of the DNA substrate strand at the rA position and release of the fluorophore and thus dramatic increase of fluorescence intensity. The sensor has a detection limit of 11 parts per trillion (45 pM), a dynamic range up to 400 nM, and selectivity of > 1-million-fold over other metal ions. The most interfering metal ion, Th(IV), interacts with the fluorescein fluorophore, causing slightly enhanced fluorescence intensity, with an apparent dissociation constant of [approximately equal to] 230 [micro]M. This sensor rivals the most sensitive analytical instruments for uranium detection, and its application in detecting uranium in contaminated soil samples is also demonstrated. This work shows that simple, cost-effective, and portable metal sensors can be obtained with similar sensitivity and selectivity as much more expensive and sophisticated analytical instruments. Such a sensor will play an important role in environmental remediation of radionuclides such as uranium. DNA | DNAzyme | fluorescence | deoxyribozyme | catalytic DNA

A Pb(II)-specific DNAzyme fuorescent sensor has been modified with a thiol moiety in order to immobilize it on a Au surface. Self-assembly of the DNAzyme is accomplished by first adsorbing the single-thiolated enzyme strand (HS-17E-Dy) followed by adsorption of mercaptohexanol, which serves to displace any Au-N interactions and ensure that DNA is bound only through the S-headgroup. The preformed self-assembled monolayer is then hybridized with the complementary fluorophore-containing substrate strand (17DS-FI). Upon reaction with Pb(II), the substrate strand is cleaved, releasing a fluorescent fragment for detection. Fluorescence intensity may be correlated with original Pb(II) concentration, and a linear calibration was obtained over nearly four decades: 10 [micro]M [greater than or equal to] [Pb(II)] [greater than or equal to] 1 nM. The immobilized DNAzyme is a robust system; it may be regenerated after cleavage, allowing multiple sensing cycles. In addition, drying of fully assembled DNAzyme before reaction with Pb(II) does not significantly affect analytical performance. These results demonstrate that, in comparison with solution-based schemes, immobilization of the DNAzyme sensor onto a Au surface lowers the detection limit (from 10 to 1 nM), maintains activity and specificity, and allows sensor regeneration and long-term storage. Realization of Pb(II) detection through an immobilized DNAzyme is the first important step toward creation of a stand-alone, portable Pb(II) detection device such as those immobilizing DNAzyme recognition motifs in the nanofluidic pores of a microfluidic-nanofluidic hybrid multilayer device.

BTEX and two chemical warfare simulants, half mustard and dissopropylmethyl phosphonate, are placed in water and adsorbed into fiberglass supported activated carbon filters. Removal of the contaminants, the pressure drops of the filters, and the regeneration of the FGAC filter is graphed.

A study was held to review the effects of surface modification of nanocrystalline titanium dioxide with certain chelating agents on photocatalytic degradation of nitrobenzene. The report is broken down into the introduction, a discussion of the experiment, and a discussion of the results.