Listeria monocytogenes and Salmonella spp. are among the most common cause of foodborne illnesses that negatively affect consumers’ health and food producers’ finances and credibility. Techniques used to detect pathogens (e.g., total viable counts, polymerase chain reaction, and enzyme-linked immunosorbent assays) are time consuming and costly as they require laboratory conditions with trained personnel. To meet this demand without compromising public health concerns, highly sensitive and rapid sensors are needed in food processing facilities for pathogen detection to reduce cost and holding time for food products. Ideally, these sensors should be small, label-free, low cost, portable, and highly sensitive/selective. This study describes some recent approaches for creating biomimetic sensors by optimizing the bacteria capture efficiency without the need for pre-concentration and pre-labeling steps. Two in-field biosensors were developed for measuring pathogenic bacteria in food matrices. The first example consists of pH-responsive polymer nanobrushes embedded with platinum nanoparticles platform with enhanced limit of detection and sensitivity for quantification of Listeria monocytogenes in fresh vegetables. A new approach using a one-step metal and polymer simultaneous deposition was tested using two pH-sensitive polymers and a thiol-terminated DNA aptamer selective to surface protein internalin A of Listeria monocytogenes. The second example demonstrates development of pathogenic biosensors for chicken broth using antibodies and DNA aptamers selective to Salmonella Typhimurium adsorbed to aerosolized graphene interdigitated electrodes (IDEs). Devices were printed in polyimide tape and aerosolized graphene was thermally annealed. The integrity of the substrate was analyzed and the nano-biosensors were characterized for topography, pH-actuation, graphene content, and electroactivity using electron microscopy, cyclic voltammetry, and multiple spectroscopy techniques (Raman, Fourier-transform infrared, and electrochemical impedance). Electrochemical impedance spectroscopy was used to evaluate the signal and determine the limit of detection by evaluating the change in charge transfer resistance. The nano-biosensors have a detection limit of approximately 5 CFU.mL-1, and a response time of approximately 17 minutes (15 minutes incubation period). The pH-sensitive nanobrushes and graphene-based biosensors have a selectivity for the target pathogen of approximately 95% in vegetable and chicken broth, respectively. The designed biosensor platform showed great potential to replace current standard methods used by the food industry for rapid foodborne pathogenic bacteria detection.
Graphene paper has diverse applications in printed circuit board electronics, bioassays, 3D cell culture, and biosensing. Although development of nanometal-graphene hybrid composites is commonplace in the sensing literature, to date there are only a few examples of nanometal-decorated graphene paper for use in biosensing. In this manuscript, we demonstrate the synthesis and application of Pt nano cauliflower-functionalized graphene paper for use in electrochemical biosensing of small molecules (glucose, acetone, methanol) or detection of pathogenic bacteria (Escherichia coli O157:H7). Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy were used to show that graphene oxide deposited on nanocellulose crystals was partially reduced by both thermal and chemical treatment. Fractal platinum nanostructures were formed on the reduced graphene oxide paper, producing a conductive paper with an extremely high electroactive surface area, confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. To show the broad applicability of the material, the platinum surface was functionalized with three different biomaterials: 1) glucose oxidase (via chitosan encapsulation); 2) a DNA aptamer (via covalent linking), or 3) a chemosensory protein (via his linking). We demonstrate the application of this device for point of care biosensing. The detection limit for both glucose (0.08 ± 0.02 μM) and E. coli O157:H7 (1.3 ± 0.1 CFU mL-1) were competitive with, or superior to, previously reported devices in the biosensing literature. The response time (6 sec for glucose and 10 min for E. coli) were also similar to silicon biochip and commercial electrode sensors. The results demonstrate that the nanocellulose-graphene-nanoplatinum material is an excellent paper-based platform for development of electrochemical biosensors targeting small molecules or whole cells for use in point of care biosensing.
Enhanced interest in wearable biosensor technology over the past decade is directly related to the increasing prevalence of diabetes and the associated requirement of daily blood glucose monitoring. In this work we investigate the platinum-carbon transduction element used in traditional first-generation glucose biosensors which rely on the concentration of hydrogen peroxide produced by the glucose–glucose oxidase binding scheme. We electrodeposit platinum nanoparticles on a commercially-available screen printed carbon electrode by stepping an applied current between 0 and 7.12 mA/cm2 for a varying number of cycles. Next, we examine the trends in deposition and the effect that the number of deposition cycles has on the sensitivity of electrochemical glucose sensing. Results from this work indicate that applying platinum nanoparticles to screen printed carbon via electrodeposition from a metal salt solution improves overall biosensor sensitivity. This work also pinpoints the amount of platinum (i.e., number of deposition cycles) that maximizes biosensor sensitivity in an effort to minimize the use of the precious metals, viz., platinum, in electrode fabrication. In summary, this work quantifies the relationship between platinum electrodeposition and sensor performance, which is crucial in designing and producing cost-effective sensors.
Listeria monocytogenes is one of the most common causes of food illness deaths worldwide, with multiple outbreaks in the United States alone. Current methods to detect foodborne pathogens are laborious and can take several hours to days to produce results. Thus, faster techniques are needed to detect bacteria within the same reliability level as traditional techniques. This study reports on a rapid, accurate, and sensitive aptamer biosensor device for Listeria spp. detection based on platinum interdigitated array microelectrodes (Pt-IDEs). Pt-IDEs with different geometric electrode gaps were fabricated by lithographic techniques and characterized by cyclic voltammetric (CV), electrochemical impedance spectroscopy (EIS), and potential amperometry (DCPA) measurements of reversible redox species. Based on these results, 50 μm Pt-IDE was chosen to further functionalize with a Listeria monocytogenes DNA aptamer selective to the cell surface protein internalin A, via metal-thiol self-assembly at the 5' end of the 47-mer's. EIS analysis was used to detect Listeria spp. without the need for label amplification and pre-concentration steps. The optimized aptamer concentration of 800 nM was selected to capture the bacteria through internalin A binding and the aptamer hairpin structure near the 3' end. The aptasensor was capable of detecting a wide range of bacteria concentration from 10 to 106 CFU/mL at lower detection limit of 5.39 ± 0.21 CFU/mL with sensitivity of 268.1 ± 25.40 (Ohms/log [CFU/mL]) in 17 min. The aptamer based biosensor offers a portable, rapid and sensitive alternative for food safety applications with one of the lowest detection limits reported to date.
Here we demonstrate a novel approach for fabricating point of care (POC) wearable electrochemical biosensors based on 3D patterning of bionanocomposite networks. To create Bio-Inspired Patterned network (BIPS) electrodes, we first generate fractal network in silico models that optimize transport of network fluxes according to an energy function. Network patterns are then inkjet printed onto flexible substrate using conductive graphene ink. We then deposit fractal nanometal structures onto the graphene to create a 3D nanocomposite network. Finally, we biofunctionalize the surface with biorecognition agents using covalent bonding. In this paper, BIPS are used to develop high efficiency, low cost biosensors for measuring glucose as a proof of concept. Our results on the fundamental performance of BIPS sensors show that the biomimetic nanostructures significantly enhance biosensor sensitivity, accuracy, response time, limit of detection, and hysteresis compared to conventional POC non fractal electrodes (serpentine, interdigitated, and screen printed electrodes). BIPs, in particular Apollonian patterned BIPS, represent a new generation of POC biosensors based on nanoscale and microscale fractal networks that significantly improve electrical connectivity, leading to enhanced sensor performance.
Enzymes are important players in multiple applications, be it bioremediation, biosynthesis, or as reporters. The business of catalysis and inhibition of enzymes is a multibillion dollar industry and understanding the kinetics of commercial enzymes can have a large impact on how these systems are optimized. Recent advances in nanotechnology have opened up the field of nanoparticle (NP) and enzyme conjugates and two principal architectures for NP conjugate systems have been developed. In the first example the enzyme is bound to the NP in a persistent manner, here we find that key factors such as directed enzyme conjugation allow for enhanced kinetics. Through controlled comparative experiments we begin to tease out specific mechanisms that may account for the enhancement. The second system is based on dynamic interactions of the enzymes with the NP. The enzyme substrate is bound to the NP and the enzyme is free in solution. Here again we find that there are many variables , such as substrate positioning and NP selection, that modify the kinetics.
Luminescent semiconductor nanocrystals or quantum dots (QDs) hold tremendous
promise for in vivo biosensing, cellular imaging, theranostics, and smart molecular sensing
probes due to their small size and favorable photonic properties such as resistance to
photobleaching, size-tunable PL, and large effective Stokes shifts. Herein, we demonstrate how
QD-based bioconjugates can be used to enhance enzyme kinetics. Enzyme-substrate kinetics are
analyzed for solutions containing both alkaline phosphatase enzymes and QDs with enzyme-to-
QD molar ratios of 2, 12, and 24 as well as for a solution containing the same concentration of
enzymes but without QDs. The enzyme kinetic paramters Vmax, KM, and Kcat/KM are extracted from the enzyme progress curves via the Lineweaver-Burk plot. Results demonstrate an
approximate increase in enzyme efficiency of 5 - 8% for enzymes immobilized on the QD
versus free in solution without QD immobilization.
Luminescent semiconductor nanocrystals or quantum dots (QDs) contain favorable photonic properties (e.g., resistance to photobleaching, size-tunable PL, and large effective Stokes shifts) that make them well-suited for fluorescence (Förster) resonance energy transfer (FRET) based applications including monitoring proteolytic activity, elucidating the effects of nanoparticles-mediated drug delivery, and analyzing the spatial and temporal dynamics of cellular biochemical processes. Herein, we demonstrate how unique considerations of temporal and spatial constraints can be used in conjunction with QD-FRET systems to open up new avenues of scientific discovery in information processing and molecular logic circuitry. For example, by conjugating both long lifetime luminescent terbium(III) complexes (Tb) and fluorescent dyes (A647) to a single QD, we can create multiple FRET lanes that change temporally as the QD acts as both an acceptor and donor at distinct time intervals. Such temporal FRET modulation creates multi-step FRET cascades that produce a wealth of unique photoluminescence (PL) spectra that are well-suited for the construction of a photonic alphabet and photonic logic circuits. These research advances in bio-based molecular logic open the door to future applications including multiplexed biosensing and drug delivery for disease diagnostics and treatment.
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