Keren Jiang

Impedimetric detection of pathogenic Gram-positive bacteria using an antimicrobial peptide from class IIa bacteriocins.

Real-time, label-free detection of Gram-positive bacteria with high selectivity and sensitivity is demonstrated using an interdigitated impedimetric array functionalized with naturally produced antimicrobial peptide from class IIa bacteriocins. The antimicrobial peptide, leucocin A, was chemically synthesized and covalently immobilized on interdigitated gold microelectrodes via the interaction between the C-terminal carboxylic acid of the peptide and free amines of a preattached thiolated linker. Exposing the peptide sensor to various concentrations of Gram-positive bacteria generated reproducible impedance spectra that detected peptide-bacteria interactions at a concentration of 1 cell/μL. The peptide sensor also selectively detected Listeria monocytogenes from other Gram-positive strains at a concentration of 10(3) cfu mL(-1). The study highlights that short peptide ligands from bacteriocin class offer high selectivity in bacterial detection and can be used in developing a robust, portable biosensor device to efficiently detect pathogenic Gram-positive bacteria in food samples.

Real-time Detection of Breast Cancer Cells Using Peptide-functionalized Microcantilever Arrays.

Ligand-directed targeting and capturing of cancer cells is a new approach for detecting circulating tumor cells (CTCs). Ligands such as antibodies have been successfully used for capturing cancer cells and an antibody based system (CellSearch®) is currently used clinically to enumerate CTCs. Here we report the use of a peptide moiety in conjunction with a microcantilever array system to selectively detect CTCs resulting from cancer, specifically breast cancer. A sensing microcantilever, functionalized with a breast cancer specific peptide 18-4 (WxEAAYQrFL), showed significant deflection on cancer cell (MCF7 and MDA-MB-231) binding compared to when exposed to noncancerous (MCF10A and HUVEC) cells. The peptide-functionalized microcantilever allowed efficient capture and detection of cancer cells in MCF7 spiked human blood samples emulating CTCs in human blood. A detection limit of 50–100 cancer cells mL−1 from blood samples was achieved with a capture yield of 80% from spiked whole blood samples. The results emphasize the potential of peptide 18-4 as a novel peptide for capturing and detecting cancer cells in conjunction with nanomechanical cantilever platform. The reported peptide-based cantilever platform represents a new analytical approach that can lead to an alternative to the various detection platforms and can be leveraged to further study CTCs.

Investigation of pH-induced protein conformation changes by nanomechanical deflection.

Broad-spectrum biosensing technologies examine sensor signals using biomarkers, such as proteins, DNA, antibodies, specific cells, and macromolecules, based on direct- or indirect-conformational changes. Here, we have investigated the pH-dependent conformational isomerization of human serum albumin (HSA) using microcantilevers as a sensing platform. Native and denatured proteins were immobilized on cantilever surfaces to understand the effect of pH on conformational changes of the protein with respect to the coupling ligand. Our results show that protonation and deprotonation of amino acid residues on proteins play a significant role in generating charge-induced cantilever deflection. Surface plasmon resonance (SPR) was employed as a complementary technique to validate the results.

Detection of Listeria monocytogenes with short peptide fragments from class IIa bacteriocins as recognition elements.

We employed a direct peptide-bacteria binding assay to screen peptide fragments for high and specific binding to Listeria monocytogenes. Peptides were screened from a peptide array library synthesized on cellulose membrane. Twenty four peptide fragments (each a 14-mer) were derived from three potent anti-listerial peptides, Leucocin A, Pediocin PA1, and Curvacin A, that belong to class IIa bacteriocins. Fragment Leu10 (GEAFSAGVHRLANG), derived from the C-terminal region of Leucocin A, displayed the highest binding among all of the library fragments toward several pathogenic Gram-positive bacteria, including L. monocytogenes, Enterococcus faecalis, and Staphylococcus aureus. The specific binding of Leu10 to L. monocytogenes was further validated using microcantilever (MCL) experiments. Microcantilevers coated with gold were functionalized with peptides by chemical conjugation using a cysteamine linker to yield a peptide density of ∼4.8×10(-3) μmol/cm2 for different peptide fragments. Leu10 (14-mer) functionalized MCL was able to detect Listeria with same sensitivity as that of Leucocin A (37-mer) functionalized MCL, validating the use of short peptide fragments in bacterial detection platforms. Fragment Leu10 folded into a helical conformation in solution, like that of native Leucocin A, suggesting that both Leu10 and Leucocin A may employ a similar mechanism for binding target bacteria. The results show that peptide-conjugated microcantilevers can function as highly sensitive platforms for Listeria detection and hold potential to be developed as biosensors for pathogenic bacteria.

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS 2 multilayers

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting1–3. A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification2. Here, we show that continuous direct-current (d.c.) with a maximum density of 106 A m−2 can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS2). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (105−106 V m−2) at the conductive nanoscale tip4. We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current−voltage spectra analysis indicates that the rectifying Schottky barrier at the tip–sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.A large triboelectric direct current can be generated via the nanoscale sliding friction of a conductive-AFM tip on a MoS2 thin film.

Freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors

Nanocellulose is a sustainable and eco-friendly nanomaterial derived from renewable biomass. In this study, we utilized the structural advantages of two types of nanocellulose and fabricated freestanding carbonized hybrid nanocellulose films as electrode materials for supercapacitors. The long cellulose nanofibrils (CNFs) formed a macroporous framework, and the short cellulose nanocrystals were assembled around the CNF framework and generated micro/mesopores. This two-level hierarchical porous structure was successfully preserved during carbonization because of a thin atomic layer deposited (ALD) Al2O3 conformal coating, which effectively prevented the aggregation of nanocellulose. These carbonized, partially graphitized nanocellulose fibers were interconnected, forming an integrated and highly conductive network with a large specific surface area of 1,244 m2·g–1. The two-level hierarchical porous structure facilitated fast ion transport in the film. When tested as an electrode material with a high mass loading of 4 mg·cm–2 for supercapacitors, the hierarchical porous carbon film derived from hybrid nanocellulose exhibited a specific capacitance of 170 F·g–1 and extraordinary performance at high current densities. Even at a very high current of 50 A·g–1, it retained 65% of its original specific capacitance, which makes it a promising electrode material for high-power applications.

Rapid and Highly Sensitive Detection of Dopamine Using Conjugated Oxaborole-Based Polymer and Glycopolymer Systems

A conjugated polymer interface consisting of an oxaborole containing polymer and a glycopolymer was used for achieving very high selectivity in dopamine (DA) detection. The optimum binding affinity between the polymers promotes the selectivity to DA through a displacement mechanism while remaining unaffected by other structurally related analogs and saccharide derivatives. Real-time detection of DA with very high selectivity and sensitivity has been demonstrated by immobilizing the polymer conjugates on surface plasmon resonance (SPR) and microcantilever (MCL) sensor platforms. Using the conjugated polymer sensing layer, the SPR biosensor was capable of detecting DA in the concentration range of 1 × 10-9 to 1 × 10-4 mol L-1, whereas the MCL sensor showed a limit of detection (LOD) of 5 × 10-11 mol L-1. We find that the sensing mechanism is based on DA-induced reversible swelling of the conjugated polymer layer and this allows regeneration and reuse of the sensor multiple times. Also, we conclude that SPR is a suitable sensor platform for DA in-line detection at clinical level considering the detection time and stability, whereas MCL can achieve a much lower LOD.

Rapid label-free detection of E. coli using antimicrobial peptide assisted impedance spectroscopy

There is an increasing demand for rapid detection of waterborne pathogens to monitor drinking water safety. We demonstrate a compact, label-free sensor array for rapid detection of Escherichia coli (E. coli) in contaminated water samples using antimicrobial peptide assisted impedimetric sensor platform. Interdigitated electrode arrays immobilized with the antimicrobial peptide Colicin V (ColV) were used to screen the affinity towards different bacterial strains by monitoring impedance variations in real-time. This ColV assisted impedance biosensor exhibited high selectivity towards Gram-negative strains particularly towards E. coli strains. This selective detection of E. coli from other strains was observed at 102 cfu mL−1, which is clinically relevant. The sensor can detect E. coli from 102 to 106 cfu mL−1 in water sample at pH 7 to 9. These results show that the antimicrobial peptide ColV assisted impedimetric array is capable of rapid, specific detection of E. coli in contaminated water samples.

Portable Nanofiber-Light Addressable Potentiometric Sensor for Rapid Escherichia coli Detection in Orange Juice

The growing need to prevent pathogen outbreaks is irrefutable in the case of the food industry. Early detection in products, especially beverages, contaminated with bacterial strains is vital to avoid infected foods from reaching the consumer. If E. coli is pesent in such foods, it can cause infections. It can also be an indicator of the existence of other harmful coliforms. In this study, we have investigated the detection of Escherichia coli ( E. coli) in orange juice using a portable nanofiber-light addressable potentiometric sensor (NF-LAPS). We have chosen electrospun pH-sensitive poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) hydrogel NFs as the sensitive layer. The successful detection of E. coli was reported with the NF-LAPS in less than 1 h. The limit of detection (LOD) measured in the sensor is found to be102 CFU/mL. We have confirmed the selectivity of the biosensor toward E. coli by examining the response of the NF-LAPS against Salmonella typhimurium ( S. typhi), also commonly found in orange juice. Despite the complex nature of orange juice, the response of the biosensor is in no way affected while orange juice is tested as is.

Modified cantilever arrays improve sensitivity and reproducibility of nanomechanical sensing in living cells

Mechanical signaling involved in molecular interactions lies at the heart of materials science and biological systems, but the mechanisms involved are poorly understood. Here we use nanomechanical sensors and intact human cells to provide unique insights into the signaling pathways of connectivity networks, which deliver the ability to probe cells to produce biologically relevant, quantifiable and reproducible signals. We quantify the mechanical signals from malignant cancer cells, with 10 cells per ml in 1000-fold excess of non-neoplastic human epithelial cells. Moreover, we demonstrate that a direct link between cells and molecules creates a continuous connectivity which acts like a percolating network to propagate mechanical forces over both short and long length-scales. The findings provide mechanistic insights into how cancer cells interact with one another and with their microenvironments, enabling them to invade the surrounding tissues. Further, with this system it is possible to understand how cancer clusters are able to co-ordinate their migration through narrow blood capillaries.Samadhan Patil et al. report a new method for improving the sensitivity and reproducibility of mechanobiological measurements in malignant cancer cells. Their findings provide insight into the interaction of cells with each other and the microenvironment and may impact our understanding of metastasis.