Electrochemical Detection of Waterborne Bacteria Using Bi-Functional Magnetic Nanoparticle Conjugates

Detection of microbial contamination in water is imperative to ensure water quality. We have developed an electrochemical method for the detection of E. coli using bi-functional magnetic nanoparticle (MNP) conjugates. The bi-functional MNP conjugates were prepared by terminal-specific conjugation of anti-E. coli IgG antibody and the electroactive marker ferrocene. The bi-functional MNP conjugate possesses both E. coli-specific binding and electroactive properties, which were studied in detail. The conjugation efficiency of ferrocene and IgG antibodies with amine-functionalized MNPs was investigated. Square-wave voltammetry enabled the detection of E. coli concentrations ranging from 101–107 cells/mL in a dose-dependent manner, as ferrocene-specific current signals were inversely dependent on E. coli concentrations, completely suppressed at concentrations higher than 107 cells/mL. The developed electrochemical method is highly sensitive (10 cells/mL) and, coupled to magnetic separation, provides specific signals within 1h. Overall, the bi-functional conjugates serve as ideal candidates for electrochemical detection of waterborne bacteria. This approach can be applied for the detection of other bacteria and viruses

Complementary Metal-Oxide-Semiconductor Integrated Carbon Nanotube Arrays: Toward Wide-Bandwidth Single-Molecule Sensing Systems

There is strong interest in realizing genomic molecular diagnostic platforms that are label-free, electronic, and single-molecule. One attractive transducer for such efforts is the single-molecule field-effect transistor (smFET), capable of detecting a single electronic charge and realized with a point-functionalized exposed-gate one-dimensional carbon nanotube field-effect device. In this work, smFETs are integrated directly onto a custom complementary metal-oxide-semiconductor chip, which results in an array of up to 6000 devices delivering a measurement bandwidth of 1 MHz. In a first exploitation of these high-bandwidth measurement capabilities, point functionalization through electrochemical oxidation of the devices is observed with microsecond temporal resolution, which reveals complex reaction pathways with resolvable scattering signatures. High-rate random telegraph noise is detected in certain oxidized devices, further illustrating the measurement capabilities of the platform

Novel Biologically Active Silver-Avidin Hybrids

Coupling of biologically active proteins, for example, enzymes and binding proteins, with metals carries huge potential inherent in the integration of these hybrids with miniaturized electronics, medical devices, and in vivo imaging. Here we propose and demonstrate feasibility of the preparation of novel, biologically active silver-avidin hybrids by electroless silver deposition directed to the surface of single, soluble avidin molecules, with retention of their solubility and highly specific biotin binding capacity. The process is based on conjugation of silver ions reducing polymers to avidin surface, followed by the addition of silver ions under mild physiological conditions. The partially overlapping silver patches thus obtained on the protein’s surface provided soluble, biologically active hybrids, retaining their specific biotin binding capability of both low-molecular-weight and high-molecular-weight biotinylated molecules and exhibiting enhanced thermal stability. The hybrids thus obtained were successfully used for molecular imaging of cancer cells prelabeled with biotinylated monoclonal antibody

In Situ Grafting of Silica Nanoparticle Precursors with Covalently Attached Bioactive Agents to Form PVA-Based Materials for Sustainable Active Packaging

Sustainable antibacterial–antioxidant films were prepared using in situ graftings of silica nanoparticle (SNP) precursors with covalently attached bioactive agents benzoic acid (ba) or curcumin (cur) on polyvinyl alcohol (PVA). The modified PVA-SNP, PVA-SNP-ba and PVA-SNP-cur films were characterized using spectroscopic, physicochemical and microscopic methods. The prepared films showed excellent antibacterial and antioxidant activity, and increased hydrophobicity providing protection from undesired moisture. The PVA-SNP-ba films completely prevented the growth of the foodborne human pathogen Listeria innocua, whereas PVA-SNP-cur resulted in a 2.5 log reduction of this bacteria. The PVA-SNP-cur and PVA-SNP-ba films showed high antioxidant activity of 15.9 and 14.7 Mm/g TEAC, respectively. The described approach can serve as a generic platform for the formation of PVA-based packaging materials with tailor-made activity tuned by active substituents on silica precursors. Application of such biodegradable films bearing safe bioactive agents can be particularly valuable for advanced sustainable packaging materials in food and medicine

Single-Molecule Reaction Chemistry in Patterned Nanowells

A new approach to synthetic chemistry is performed in ultraminiaturized, nanofabricated reaction chambers. Using lithographically defined nanowells, we achieve single-point covalent chemistry on hundreds of individual carbon nanotube transistors, providing robust statistics and unprecedented spatial resolution in adduct position. Each device acts as a sensor to detect, in real-time and through quantized changes in conductance, single-point functionalization of the nanotube as well as consecutive chemical reactions, molecular interactions, and molecular conformational changes occurring on the resulting single-molecule probe. In particular, we use a set of sequential bioconjugation reactions to tether a single-strand of DNA to the device and record its repeated, reversible folding into a G-quadruplex structure. The stable covalent tether allows us to measure the same molecule in different solutions, revealing the characteristic increased stability of the G-quadruplex structure in the presence of potassium ions (K⁺) versus sodium ions (Na⁺). Nanowell-confined reaction chemistry on carbon nanotube devices offers a versatile method to isolate and monitor individual molecules during successive chemical reactions over an extended period of time