Quartz Crystal Microbalance Detection of Poly(ADP-ribose) Polymerase-1 Based on Gold Nanorods Signal Amplification.

Recent findings have thrust poly(ADP-ribose) polymerase-1 (PARP-1) into the limelight as a potential biomarker and chemotherapeutic target for cancer. Thus, a sensitive method for detection of PARP-1 is necessary for early diagnosis of cancer and drug development. However, the poor electrochemical and optical activity of PARP-1 and its product poly(ADP-ribose) (PAR) prompted researchers to develop more methods. Here, we developed an efficient method for the determination of PARP-1 by using quartz crystal microbalance (QCM) because it is mass-sensitive. Once activated by the specific DNA, PARP-1 cleaves nicotinamideadenine dinucleotide (NAD+) into nicotinamide and ADP-ribose to synthesize a hyperbranched poly(ADP-ribose) polymer. Although QCM is mass-sensitive, it is not sensitive enough to discern PAR effectively. So, positively charged cetyltrimethylammonium bromide (CTAB)-coated gold nanorods (GNRs) were introduced to increase the frequency change significantly because of the strong electrostatic interaction between them with negatively charged PAR. PARP-1 ranging from 0.06 to 3 nM can be facilely detected with a low detection limit of 0.04 nM. The strategy has been used to evaluate PARP-1 inhibitors and to detect PARP-1 activity in real cancer cells lysate with satisfactory results, indicating that it was a promising candidate for clinical diagnosis and drug screening in the future.

Molecularly imprinted polymer based quartz crystal microbalance sensor for the clinical detection of insulin.

In this study, quartz crystal microbalance sensors based on molecular imprinting technology were fabricated for real-time detection of insulin in aqueous solution and artificial plasma. This study describes the preparation of insulin imprinted poly(hydroxyethyl methacrylate)-N-methacryloyl-(l)-histidine methyl ester based quartz crystal microbalance sensor for insulin determination. Poly(hydroxyethyl methacrylate)-N-methacryloyl-(l)-histidine methyl ester based film on chip surface was synthesized by ultra violet (UV) polymerization for the detection of insulin at low concentrations. At the first step, N-methacryloyl-(l)-histidine methyl ester complex was formed with insulin and then, the insulin imprinted film has been prepared. The characterization of the polymeric film has been conducted with ellipsometry, contact angle, Fourier transform infrared-attenuated total reflectance and atomic force microscopy measurements. Langmuir, Freundlich and Langmuir-Freundlich adsorption isotherm models were applied for this system. The best fitted model to explain the interactions between molecular imprinted chip and insulin molecules was the Langmuir adsorption isotherm (R2: 0.999). The repeatability of insulin imprinted chip was investigated by using of equilibration-binding-regeneration cycles for four times. The detection limit was found as 0.00158 ng/mL. According to the results, the QCM sensor has showed low-detection limit, high selectivity and sensitivity for insulin assay.

Fluid dynamics modeling for synchronizing surface plasmon resonance and quartz crystal microbalance as tools for biomolecular and targeted drug delivery studies.

We have used computational fluid dynamics modeling (CFD) to synchronize the flow conditions in the flow channels of two complementary surface-sensitive characterization techniques: surface plasmon resonance (SPR) and quartz crystal microbalance (QCM). Since the footprint of the flow channels of the two devices is specified by their function, the flow behavior can only be varied either by altering the height of the flow channel, or altering the volumetric rate of flow (flow rate) through the channel. The relevant quantity that must be calibrated is the shear strain on the measurement surface (center and bottom) of the flow channel. Our CFD modeling shows that the flow behavior is in the Stokes flow regime. We were thus able to generate a scaling expression with parameters for flow rate and flow channel height for each of the two devices: f(QCM)=2.64f(SPR)(h(QCM)/h(SPR)(2), where f(QCM) and f(SPR) are the flow rates in the SPR and QCM flow channels, respectively, and h(QCM)/h(SPR) is the ratio of the heights of the two channels. We demonstrate the success of our calibration procedure through the combined use of commercially available SPR and QCM flow channel devices on both a biomolecular interaction system of surface immobilized biotin and streptavidin and a targeted drug delivery model system of biotinylated liposomes interacting with a streptavidin functionalized surface.

Piezoelectric immunosensor for direct and rapid detection of staphylococcal enterotoxin A (SEA) at the ng level.

A direct, label-free immunosensor was designed for the rapid detection and quantification of staphylococcal enterotoxin A (SEA) in buffered solutions using quartz crystal microbalance with dissipation (QCM-D) as transduction method. The sensing layer including the anti-SEA antibody was constructed by chemisorption of a self-assembled monolayer of cysteamine on the gold electrodes placed over the quartz crystal sensor followed by activation of the surface amino groups with the rigid homobifunctional cross-linker 1,4-phenylene diisothiocyanate (PDITC) and covalent linking of binding protein (protein A or protein G). Four anti-SEA antibodies (two of which from commercial source) have been selected to set up the most sensitive detection device. With the optimized sensing layer, a standard curve for the direct assay of SEA was established from QCM-D responses within a working range of 50-1000 or 2000 ngml(-1) with a detection limit of 20 ngml(-1). The total time for analysis was 15 min. Using a sandwich type assay, the response was ca. twice higher and consequently the lowest measurable concentration dropped down to 7 ngml(-1) for a total assay time of 25 min.

Acoustic sensing of the bacterium-substratum interface using QCM-D and the influence of extracellular polymeric substances.

It is commonly assumed that bacterial presence on a QCM sensor-surface is associated with a negative frequency shift according to conventional mass-loading theory. Here, we demonstrate that bacteria adhering to QCM sensor-surface may yield positive frequency shifts up to 1.9×10(-6) Hz per bacterium according to a coupled-oscillator theory. Furthermore, it is demonstrated that the excretion of extracellular polymeric substances (EPS) by adhering bacteria can change the frequency shift in the negative direction by 1.7×10(-6) Hz per bacterium, according to conventional mass-loading theory. The difference in frequency shifts between an EPS-producing and a non-EPS producing staphylococcal strain correlated with the excretion of 3×10(-14) g EPS per bacterium, representing only a few percent of the weight of a bacterium. Thus an adsorbed molecular mass as low as a few percent of the mass of an adhering bacterium significantly alters the QCM-signal. Since adhesion of many different bacterial strains is accompanied by molecular adsorption of EPS, with potentially opposite effects on the QCM-signal, a combination of the coupled-oscillator and normal mass-loading theory has to be applied for proper interpretation of QCM-frequency shifts in bacterial detection.