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An immunosensor based on a Love-wave device and a PDMS microfluidic chip has been developed to detect potentially pathogenic microorganisms in real time. In order to characterize and test the immunosensor, the M13 bacteriophage has been chosen as a model of microorganism. The M13 was detected with the mouse monoclonal antibody, anti-M13 (AM13), which has been immobilized on the Love wave-device. The immunoassay has been carried out in a dynamic mode (continuous flow) through microchannels with the goal of obtaining a short response time in detecting a small volume of a sample of M13 bacteriophage. The concentrations of the bacteriophage have been varied between 5×108 pfuml−1 and 2×1010 pfuml−1, a range for which a fast detection and a favorable discrimination among concentrations have been achieved. The AM13 has been also used as a secondary antibody in order to measure lower concentrations such as 5×107 pfuml−1. The Double-Layer Agar technique has been used to quantify, as plaques-forming unit (pfu), the number of M13 bacteriophage in the initial sample as well as those linked to the sensor surface during the detection. Finally, the number of bacteriophage was estimated by calculating the mass sensitivity. The values obtained in both procedures have been very similar. [ABSTRACT FROM AUTHOR]

Abstract: Love wave acoustic delay lines were used as sensors for okadaic acid immuno-detection through immobilized specific antibodies. Anti-okadaic acid antibodies were grafted onto the sensor surface. Antibodies, saturating agent, and target species, okadaic acid (test line) or an irrelevant peptide (control line), were injected through an optimized microfluidic chip. Similarly to sandwich ELISA, polyclonal antibodies were then injected a second time to bind to the acid. They led to frequency shifts three times superior with okadaic acid than with the peptide. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the detection of okadaic acid (OA) as a Diarrheic Shellfish Poisoning (DSP) toxin with an acoustic wave platform in real-time. According to the FDA, the threshold for safe consumption of shellfish is 20μg of OA for 100g of shellfish tissue. The high gravimetric sensitivity of Love wave acoustic devices allow, in liquid media, immuno-detection thanks to immobilized specific antibodies. The biosensor is composed of two lines, one for the test and one used as a reference. Sensitive films were deposited through a PolyDiMethylSiloxane (PDMS) microfluidic chip. On both lines, anti-okadaic acid antibodies (OA-Ab) and saturating agents were successively injected under continuous flow with controlled flow rate. On the test line, okadaic acid (OA) was injected while an unspecific peptide (6×Histidine, 6×His) was used on the control line. On both lines, polyclonal OA-Ab were re-injected a second time to reveal previously fixed OA on the test line. Measured frequency shifts were three times higher on test lines than on control lines. In these conditions, for only 2μg of OA used for detection, the acoustic wave platform could detect DSP toxins with only 10g of shellfish tissue. [Copyright &y& Elsevier]

Abstract: The present work deals with the development of a Love-wave bacteria-based sensor platform for the detection of heavy metals in liquid medium. The acoustic delay-line is inserted in an oscillation loop in order to record the resonance frequency in real-time. A Polydimethylsiloxane (PDMS) chip with a liquid chamber is maintained by pressure above the acoustic wave propagation path. Bacteria (Escherichia coli) were fixed as bioreceptors onto the sensitive surface of the sensor coated with a polyelectrolyte (PE) multilayer using a simple and efficient layer-by-layer (LbL) electrostatic self-assembly procedure. Poly(allylamine hydrochloride) (PAH cation) and poly(styrene sulfonate) (PSS anion) were alternatively deposited so that the strong attraction between oppositely charged polyelectrolytes resulted in the formation of a (PAH-PSS) n -PAH molecular multilayer. The real-time characterization of PE multilayer and bacteria deposition is based on the measurement of the resonance frequency perturbation due to mass loading during material deposition. Real-time response to various concentrations of cadmium (Cd2+) and mercury (Hg2+) has been investigated. A detection limit as low as 10−12 mol/l has been achieved, above which the frequency increases gradually up to 10−3 mol/l, after a delay of 60s subsequent to their introduction onto bacterial cell-based biosensors. Beyond a 10−3 mol/l a steep drop in frequency was observed. This response has been attributed to changes in viscoelastic properties, related to modifications in bacteria metabolism. [ABSTRACT FROM AUTHOR]

Love wave sensors (ST-cut quartz substrate with interdigital transducers, SiO2 guiding layer and sensitive coating) have been receiving a great deal of attention for a few years. Indeed, the wave coupled in a guiding layer confers a high gravimetric sensitivity and the shear horizontal (SH) polarization allows to work in liquid media. In this paper, an analytical method is proposed to calculate the Love wave phase velocity and the gravimetric sensitivity for a complete multilayer structure. This allows us to optimize the Love wave devices design in order to improve their gravimetric sensitivity in liquid media. As a model for virus or bacteria detection in liquids (drinking or bathing water, food…) we design a model using M13 bacteriophage. The first step is the anti-M13 (AM13) monoclonal antibody grafting, on the device surface (SiO2). The second step is an immunoreaction in between the M13 bacteriophage and the AM13 antibody. The Love wave device allows to detect in real time the graft of the AM13 sensitive coating, as well as the immobilization of the M13 bacteriophages. With a pH change, the M13 bacteriophages can be removed from the sensor surface, in order to be numerated as plaque forming unit (pfu). Results on the sensitivity of Love waves are compared with similar immunological works with bulk acoustic wave devices, and demonstrate the high potentialities of Love waves sensors. [Copyright &y& Elsevier]