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The desire to translate biosensors for real time molecular monitoring has intensified due to the commercial success of 2-week continuous glucose monitors. However, a common limitation for emerging biosensors is that their lifetimes are often too short for commercially expected benchmarks of at least 3-day and ideally 2-week operation. Electrochemical sensors remain the preferred format of biochemical sensing thanks to their low cost, size, weight, and power requirements for mobile deployment. When exposed to biological fluid, all electrochemical sensors require a blocking layer to protect the electrode surface from fouling and redox interferents. Traditional blocking layer approaches rely on self-assembled monolayers which are often fragile to biological interferents like proteins and require specific electrode materials to improve their stability. Presented here is an evaluation of ultra-thin inorganic oxide and nitride films as an alternative to self-assembled monolayer blocking layers. Specifically, silicon oxide, silicon nitride, and aluminum oxide films were deposited by electron beam evaporation or atomic layer deposition at thicknesses of several nanometers to mimic the electrical capacitance of a conventional monolayer blocking layer. These oxide films were characterized over 7-days and demonstrated to provide poor protection against interfering redox currents from dissolved ferricyanide (150 - 300 µA/cm2) and oxygen reduction interference (30 - 60 µA/cm2). The oxide films were then used as a blocking layer in an electrochemical aptamer sensor using the previously published aptamer for phenylalanine. The phenylalanine sensor showed a binding affinity stronger than found in literature, but a reduced signal gain (∼ 20 % change in methylene blue redox current compared to the expected 50 % previously published on gold). It is speculated and supported by literature that these oxide and nitride films gradually dissolve over periods of days in an aqueous environment. Results further show that if lower quality oxide or nitride films are used, they may be more stable, but at the cost of initially higher in currents. While oxide and nitride films fail to improve upon the performance of thiol-blocking layers on gold electrodes, they may provide utility in some applications by allowing for alternate electrode materials and surfaces to be used instead of traditional self-assembled monolayers on gold electrodes. 

The physical properties of in vitro iron-reconstituted and genetically engineered human heteropolymer ferritins were investigated. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy-loss spectroscopy (EELS), and 57 Fe Mössbauer spectroscopy were employed to ascertain (1) the microstructural, electronic, and micromagnetic properties of the nanosized iron cores, and (2) the effect of the H and L ferritin subunit ratios on these properties. Mössbauer spectroscopic signatures indicate that all iron within the core is in the high spin ferric state. Variable temperature Mössbauer spectroscopy for H-rich (H 21 /L 3 ) and L-rich (H 2 /L 22 ) ferritins reconstituted at 1000 57 Fe/protein indicates superparamagnetic behavior with blocking temperatures of 19 K and 28 K, while HAADF-STEM measurements give average core diameters of (3.7 ± 0.6) nm and (5.9 ± 1.0) nm, respectively. Most significantly, H-rich proteins reveal elongated, dumbbell, and crescent-shaped cores, while L-rich proteins present spherical cores, pointing to a correlation between core shape and protein shell composition. Assuming an attempt time for spin reversal of τ 0 = 10 −11 s, the Néel–Brown formula for spin-relaxation time predicts effective magnetic anisotropy energy densities of 6.83 × 10 4 J m −3 and 2.75 × 10 4 J m −3 for H-rich and L-rich proteins, respectively, due to differences in surface and shape contributions to magnetic anisotropy in the two heteropolymers. The observed differences in shape, size, and effective magnetic anisotropies of the derived biomineral cores are discussed in terms of the iron nucleation sites within the interior surface of the heteropolymer shells for H-rich and L-rich proteins. Overall, our results imply that site-directed nucleation and core growth within the protein cavity play a determinant role in the resulting core morphology. Our findings have relevance to iron biomineralization processes in nature and the growth of designer's magnetic nanoparticles within recombinant apoferritin nano-templates for nanotechnology. 

Electrochemical biosensors promise a simple method to measure analytes for both point-of-care diagnostics and continuous, wearable biomarker monitors. In a liquid environment, detecting the analyte of interest must compete with other solutes that impact the background current, such as redox-active molecules, conductivity changes in the biofluid, water electrolysis, and electrode fouling. Multiple methods exist to overcome a few of these challenges, but not a comprehensive solution. Presented here is a combined boron-doped diamond electrode and oil–membrane protection approach that broadly mitigates the impact of biofluid interferents without a biorecognition element. The oil–membrane blocks the majority of interferents in biofluids that are hydrophilic while permitting passage of important hydrophobic analytes such as hormones and drugs. The boron-doped diamond then suppresses water electrolysis current and maintains peak electrochemical performance due to the foulant-mitigation benefits of the oil–membrane protection. Results show up to a 365-fold reduction in detection limits using the boron-doped diamond electrode material alone compared with traditional gold in the buffer. Combining the boron-doped diamond material with the oil–membrane protection scheme maintained these detection limits while exposed to human serum for 18 h. 

Abstract Chemical sensors based on solution‐processed 2D nanomaterials represent an extremely attractive approach toward scalable and low‐cost devices. Through the implementation of real‐time impedance spectroscopy and development of a three‐element circuit model, redox exfoliated MoS₂nanoflakes demonstrate an ultrasensitive empirical detection limit of NO₂gas at 1 ppb, with an extrapolated ultimate detection limit approaching 63 ppt. This sensor construct reveals a more than three orders of magnitude improvement from conventional direct current sensing approaches as the traditionally dominant interflake interactions are bypassed in favor of selectively extracting intraflake doping effects. This same approach allows for an all solution‐processed, flexible 2D sensor to be fabricated on a polyimide substrate using a combination of graphene contacts and drop‐casted MoS₂nanoflakes, exhibiting similar sensitivity limits. Finally, a thermal annealing strategy is used to explore the tunability of the nanoflake interactions and subsequent circuit model fit, with a demonstrated sensitivity improvement of 2× with thermal annealing at 200 °C.