Cold Atmospheric Plasma-Assisted Direct Deposition of Polypyrrole-Ag Nanocomposites for Flexible Electronic Sensors.

Conductive polymers and their composite materials have attracted considerable interest due to their potential applications in sensors, actuators, drug delivery systems, and energy storage devices. Despite their wide range of applications, many challenges remain primarily with respect to the complex synthesis and time-consuming manufacturing steps that are often required in the fabrication process of various devices with conductive polymers. Here, we demonstrate the novel use of cold atmospheric plasma (CAP)-assisted deposition technologies as a solvent-free and scalable approach for in situ polymerization and direct deposition of conductive polypyrrole-silver (PPy-Ag) nanocomposites onto the desired substrates under atmospheric conditions. In this study, a systematic approach with different precursor composition mixtures containing pyrrole as the monomer and AgNO3 as the photoinitiator was investigated to assess the effect of precursor composition on the final chemical, electrical, and mechanical properties of the PPy-Ag nanocomposite thin-film coatings which were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and cyclic bending tests. The characterizations indicated the possibility of fabricating PPy-Ag nanocomposite films with tunable degrees of polymerization and Ag nanoparticle loading by simply varying the percentage of AgNO3 in precursor composition mixtures. Finally, as a proof of concept, the potential use of the PPy-Ag nanocomposite films with different Ag nanoparticle loading percentages was assessed for humidity sensing by measuring their level of change in electrical resistance in the relative humidity range of 12-60%. It is envisioned that the developed CAP-assisted deposition technology can provide a new stepping stone toward scalable additive manufacturing of various functional nanocomposite films for different low-cost and flexible electronic applications.

Simultaneous colorimetric and electrochemical detection of trace mercury (Hg2+) using a portable and miniaturized aptasensor.

We report a novel aptasensor for the simultaneous colorimetric and electrochemical detection of mercury (Hg2+). This device consists of a paper-based microfluidic component (µ-PAD) incorporated into a miniaturized three-electrode system fabricated through printed circuit board (PCB) technology. This biosensor is portable, rapid, versatile, and can detect Hg2+ down to 0.01 ppm based on 3σ of the blank/slope criteria. Moreover, it is highly selective against As2+, Cu2+, Zn2+, Pb2+, Cd2+, Mg2+, and Fe2+, reaching up to 13 times more of the input signal than the other heavy metals. The colorimetric detection mechanism uses aptamer functionalized polystyrene (PS)-AgNPs and Ps-AuNPs microparticles' specific aggregation. The Ps-AuNPs-based system allows qualitative detection (LOD 5 ppm) and stability over seven days (up to 97.59% signal retention). For the Ps-AgNPs-based system, the detection limit is 0.5 ppm with a linear range from 0.5 to 20 ppm (adjusted R2= 0.986) and stability over 30 days (up to 94.95% signal retention). The electrochemical component measures changes in charge transfer resistance upon target-aptamer hybridization using a [Ru (NH3)6]3+Cl3] redox probe. The latest component presents a linear range from 0.01 to 1 ppm (adjusted R2= 0.935) with a LOD of 0.01 ppm and performance stability over seven days (up to 102.52 ± 11.7 signal retention). This device offers a universal dual detection platform with multiplexing, multi-replication, quantitative color analysis, and minimization of false results. Furthermore, detection results in river samples showed recoveries up to 91.12% (RSD 0.85) and 105.61% (RSD 1.62) for the electrochemical and colorimetric components, respectively. The proposed system is highly selective with no false-positive or false-negative results in an overall wide linear range and can safeguard the accuracy of detection results in aptasensing platforms in general.

Microfluidic paper-based aptasensor devices for multiplexed detection of pathogenic bacteria.

Foodborne pathogens are major public health concerns worldwide. Paper-based microfluidic devices are versatile, user friendly and low cost. We report a novel paper-based single input channel microfluidic device that can detect more than one whole-cell foodborne bacteria at the same time, and comes with quantitative reading via image analysis. This microfluidic paper-based multiplexed aptasensor simultaneously detects E. coli O157:H7 and S. Typhimurium. Custom designed particles provide colorimetric signal enhancement and false results prevention. Several aptamers were screened and the highest-affinity aptamers were optimized and employed for detection of these bacteria in solution, both in a buffer as well as pear juice. Image analysis was used to read and quantify the colorimetric signal and measure bacteria concentration, thus rendering this paper based microfluidic device quantitative. The colorimetric results show linearity over a wide concentration range (102CFU/mL to 108CFU/mL) and a limit of detection (LOD) of 103CFU/mL and 102CFU/mL for E. coli O157:H7 and S. Typhimurium, respectively. An insignificant change in colorimetric response for non-target bacteria indicates the aptasesnors are specific. The reported multiplexed colorimetric paper-based microfluidic devices is likely to perform well for on-site rapid screening of pathogenic bacteria in water and food products.

DNA-Functionalized Ti3C2Tx MXenes for Selective and Rapid Detection of SARS-CoV-2 Nucleocapsid Gene.

Coronavirus disease 2019 (COVID-19) is an emerging human infectious disease caused by severe acute respiratory syndrome 2 (SARS-CoV-2, initially called novel coronavirus 2019-nCoV) virus. Thus, an accurate and specific diagnosis of COVID-19 is urgently needed for effective point-of-care detection and disease management. The reported promise of two-dimensional (2D) transition-metal carbides (Ti3C2Tx MXene) for biosensing owing to a very high surface area, high electrical conductivity, and hydrophilicity informed their selection for inclusion in functional electrodes for SARS-CoV-2 detection. Here, we demonstrate a new and facile functionalization strategy for Ti3C2Tx with probe DNA molecules through noncovalent adsorption, which eliminates expensive labeling steps and achieves sequence-specific recognition. The 2D Ti3C2Tx functionalized with complementary DNA probes shows a sensitive and selective detection of nucleocapsid (N) gene from SARS-CoV-2 through nucleic acid hybridization and chemoresistive transduction. The fabricated sensors are able to detect the SARS-CoV-2 N gene with sensitive and rapid response, a detection limit below 105 copies/mL in saliva, and high specificity when tested against SARS-CoV-1 and MERS. We hypothesize that the MXenes' interlayer spacing can serve as molecular sieving channels for hosting organic molecules and ions, which is a key advantage to their use in biomolecular sensing.

Recent Advances in Aptamer-Based Biosensors for Global Health Applications.

Since aptamers were first reported in the early 2000s, research on their use for the detection of health-relevant analytical targets has exploded. This review article provides a brief overview of the most recent developments in the field of aptamer-based biosensors for global health applications. The review provides a description of general aptasensing principles and follows up with examples of recent reports of diagnostics-related applications. These applications include detection of proteins and small molecules, circulating cancer cells, whole-cell pathogens, extracellular vesicles, and tissue diagnostics. The review also discusses the main challenges that this growing technology faces in the quest of bringing these new devices from the laboratory to the market.

Microencapsulation of reuterin to enhance long-term efficacy against food-borne pathogen Listeria monocytogenes.

The aim of this study was to microencapsulate the reuterin produced by Lactobacillus reuteri BPL-36 strain for its long-term efficacy against food-borne pathogen Listeria monocytogenes. Lactobacillus reuteri BPL-36 strain previously isolated from a human infant fecal sample in lab was selected for the present study based on its ability to produce reuterin. The organism displayed a broad-spectrum antimicrobial activity. Reuterin concentration of 89.63 mM was obtained in the MRS-glycerol medium after 16 h incubation at 37 °C. The reuterin concentration required to inhibit the growth of Pseudomonas aeruginosa, Escherichia coli O157: H7, Salmonella typhi, Staphylococcus aureus, and Listeria monocytogenes was found to be 1.0, 2.0, 2.0, 4.0, and 10.0 AU/mL, respectively. Microencapsulation of reuterin to enhance long-term efficacy against food-borne pathogens was done. Results in this study indicated that the release characteristics of reuterin from the encapsulated particles were pH dependent. The release characteristics were unaffected by the storage of encapsulated reuterin at 4 °C for 2 weeks. The anti-listerial efficacy of the encapsulated reuterin was tested against L. monocytogenes in the BHI medium adjusted to pH 5.0 with a reuterin content equivalent to 16 mM, similar to un-encapsulated (free) reuterin. Encapsulated reuterin demonstrated enhanced efficacy against L. monocytogenes for longer duration of time when compared with un-encapsulated (free) reuterin. The present work demonstrated a novel antimicrobial delivery system that ensured much better capability of inhibiting the growth of L. monocytogenes throughout 24 h incubation at 37 °C.

Fat accumulation in differentiated brown adipocytes is linked with expression of Hox genes.

Homeobox (Hox) genes are involved in body plan of embryo along the anterior-posterior axis. Presence of several Hox genes in white adipose tissue (WAT) and brown adipose tissue (BAT) is indicative of involvement of Hox genes in adipogenesis. We propose that differentiation inducing agents viz. isobutyl-methyl-xanthine (IBMX), indomethacin, dexamethasone (DEX), triiodothyronine (T3) and insulin may regulate differentiation in brown adipose tissue through Hox genes. In vitro culture of brown fat stromalvascular fraction (SVF) in presence or absence of differentiation inducing agents was used for establishing relationship between fat accumulation in differentiated adipocytes and expression of Hox genes. Relative expression of Pref1, UCP1 and Hox genes was determined in different stages of adipogenesis. Presence or absence of IBMX, indomethacin and DEX during differentiation of proliferated pre-adipocytes resulted in marked differences in expression of Hox genes and lipid accumulation. In presence of these inducing agents, lipid accumulation as well as expression of HoxA1, HoxA5, HoxC4 &HoxC8 markedly enhanced. Irrespective of presence or absence of T3, insulin down regulates HoxA10. T3 results in over expression of HoxA5, HoxC4 and HoxC8 genes, whereas insulin up regulates expression of only HoxC8. Findings suggest that accumulation of fat in differentiated adipocytes is linked with expression of Hox genes.

A rapid paper chromatographic method for detection of anionic detergent in milk.

A paper chromatographic method for the detection of adulteration of anionic detergent in milk is described. The method is based on the complexing of anionic detergent with methylene blue dye and separation of complex from free dye using simple paper chromatographic method. Since complexing of detergent is with dye, visualization is direct without involvement of subsequent detection of complex. The method is simple and results are available in 10 min. The method is sensitive to detect 0.1 % (w/v) labolene (laboratory grade detergent) or 0.01 % (w/v) sodium dodecylbenzene sulfonate (pure anionic detergent) in milk. The method can be adopted at quality control laboratories in dairies for ascertaining the quality of milk.