ABSTRACT
The sensitivity and performance of an asymmetric Mach-Zehnder interferometer (aMZI) were compared to those of quartz crystal microbalance with dissipation (QCM-D). The binding of streptavidin to sensor chips coated with poly-l-lysine (PLL), modified with biotin and oligoethyleneglycol (OEG) (PLL-biotin), was used to compare the binding signals obtained from both technologies. PLL-biotin proved to be an efficient method to add bioreceptors to both the QCM-D and aMZI chips. The final, saturated value of streptavidin binding was compared with those from aMZI (253 ng cm-2) and QCM-D (460 ng cm-2). These values were then used to evaluate that 45% of the measured streptavidin mass in the QCM-D came from hydrodynamically coupled water. Importantly, the signal-to-noise ratio of the aMZI was found to be 200 times higher than that of the QCM-D. These results indicate the potential of the aMZI platform for highly sensitive and accurate biosensing applications.
ABSTRACT
Aflatoxins (AF) are naturally occurring mycotoxins, produced by many species of Aspergillus. Among aflatoxins, Aflatoxin M1 (AFM1) is one of the most frequent and dangerous for human health. The acceptable maximum level of AFM1 in milk according to EU regulation is 50 ppt, equivalent to 152 pM, and 25 ppt, equivalent to 76 pM, for adults and infants, respectively. Here, we study a photonic biosensor based on Si 3 N 4 asymmetric Mach-Zehnder Interferometers (aMZI) functionalized with Fab' for AFM1 detection in milk samples (eluates). The minimum concentration of AFM1 detected by our aMZI sensors is 48 pM (16.8 pg/mL) in purified and concentrated milk samples. Moreover, the real-time detection of the ligand-analyte binding enables the study of the kinetics of the reaction. We measured the kinetic rate constants of the Fab'-AFM1 interaction.
Subject(s)
Aflatoxin M1/analysis , Biosensing Techniques , Food Contamination/analysis , Milk/chemistry , Aflatoxin M1/chemistry , Aflatoxin M1/immunology , Animals , Enzyme-Linked Immunosorbent Assay , Immunoglobulin Fab Fragments/chemistry , Immunoglobulin Fab Fragments/immunology , Interferometry , Light , Silicon Compounds/chemistryABSTRACT
In order to realize the multi-analyte assays for environmental contaminants, an optical biosensor utilizing laser-induced fluorescence-based detection via the binding of biomolecules to the surface of an integrated TriPleX™ waveguide chip on a glass substrate (fused silica, FS) is described. As far as we know, this is the first demonstration of using the TriPleX™ technology to fabricate the waveguide chip on a FS substrate. The sensor consists of 32 individually addressable sensor patches, which were formed on the chip surface by exploiting 3 Y-junction splitters, creating four equal rows of eight evanescently excited windows in parallel. The basic low-loss SiO2/Si3N4 TriPleX™ waveguide configuration in combination with on-chip spotsize convertors allows for both high fiber-to-chip coupling efficiency and enables at the same time individually optimized high chip surface intensity and low patch-to-patch deviation. Moreover, the complementary metal-oxide-semiconductor compatible fabrication of waveguide chip allows for its mass production at low cost. By taking MC-LR, 2,4-D, atrazine and BPA as the model analytes, the as-proposed waveguide based biosensor was proven sensitive with the detection limits of 0.22⯵g/L for MC-LR, 1.18⯵g/L for 2, 4-D, 0.2⯵g/L for atrazine and 0.06⯵g/L for BPA. Recoveries of the biosensor towards simultaneous detection of MC-LR, 2, 4-D, atrazine and BPA in spiked real water samples varied from 84% to 120%, indicating the satisfactory accuracy of the established technology.
Subject(s)
Atrazine/isolation & purification , Biosensing Techniques , Environmental Pollutants/isolation & purification , Atrazine/toxicity , Environmental Pollutants/toxicity , Fluorescence , Lasers , Silicon Dioxide/chemistryABSTRACT
In this work, we present a study of Aflatoxin M1 detection by photonic biosensors based on Si3N4 Asymmetric Mach-Zehnder Interferometer (aMZI) functionalized with antibodies fragments (Fab'). We measured a best volumetric sensitivity of 104 rad/RIU, leading to a Limit of Detection below 5 × 10(-7) RIU. On sensors functionalized with Fab', we performed specific and non-specific sensing measurements at various toxin concentrations. Reproducibility of the measurements and re-usability of the sensor were also investigated.
Subject(s)
Aflatoxin M1/isolation & purification , Biosensing Techniques/instrumentation , Silicon Compounds/chemistry , Interferometry , Optical Phenomena , Photons , Reproducibility of ResultsABSTRACT
Combining reaction and detection in multiphase microfluidic flow is becoming increasingly important for accelerating process development in microreactors. We report the coupling of UV/Vis spectroscopy with microreactors for online process analysis under segmented flow conditions. Two integration schemes are presented: one uses a cross-type flow-through cell subsequent to a capillary microreactor for detection in the transmission mode; the other uses embedded waveguides on a microfluidic chip for detection in the evanescent wave field. Model experiments reveal the capabilities of the integrated systems in real-time concentration measurements and segmented flow characterization. The application of such integration for process analysis during gold nanoparticle synthesis is demonstrated, showing its great potential in process monitoring in microreactors operated under segmented flow.