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Nanomaterials-based bioinspired enzyme mimics are gaining increased attention as alternatives to biocatalysts. Herein, we report synthesizing oxygen-terminated few-layered titanium-based MXene nanosheets (OFL-Ti-MN). OFL-Ti-MN possesses horseradish peroxidase (HRP) activity in catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H

The COVID-19 pandemic has caused a dramatic increase in plastic wastes associated with the use of single-use masks, gloves, gowns, and other personal protective equipment (PPE). The accumulation of PPE, especially single-use masks, end up polluting environment, causing harm mainly to aquatic and terrestrial ecosystems. Due to the enormous concern about plastic pollution, many efforts are being made to develop efficient technologies to tackle it, among which solid-state photocatalysis is highlighted. Even though the outstanding results that have been obtained with the solid-state application of photocatalysis, there are fewer publications and reports on the use of it in comparison with aqueous and/or gaseous phase photocatalysis. Then, this review presents the most relevant works published on this topic and provide an in-depth analysis of solid-state photocatalysis for plastic abatement, including the incorporation of the usually hydrophilic photocatalyst into the hydrophobic plastic matrix, the common experimental procedures for evaluating its effectiveness (gravimetric, optical, spectroscopic, and mechanical methods) and the description of the intricate reaction mechanism suggested so far. The aim is increasing the awareness on this innovative topic among the academic/industrial community and advancing the research thereon.

Sadak, Ömer; Ardahan Üniversitesi - Mühendislik Fakültesi - Elektrik-Elektronik Mühendisliği Bölümü - Elektronik Anabilim Dalı - Makale, We describe a simple strategy to modify zeolitic imidazolate framework-8 (ZIF-8) using polyaniline (PANI) via a controlled interfacial polymerization method, without using a template, to synthesize ZIF-8/PANI nanocomposites. Our method avoids the agglomeration of ZIF-8/PANI, boosts the utilization of active materials, and exposes more active sites, and hence, it is advantageous to facile electron transfer. Because of its unique hierarchical structure, ZIF-8/ PANI has a high surface area (610.8 m2·g−1) and the ZIF-8/PANI electrode exhibited a capacitance value of 395.4 F·g−1 at 0.2 A·g−1, which is the highest among the metal−organic framework (MOF)-based composites reported to date. A solid-state asymmetric supercapacitor (SASC) fabricated with ZIF-8/PANI as the electrode showed good capacitive behavior over a wide potential window from 0 to 2.5 V without nonaqueous electrolytes. It exhibited a specific areal capacitance of 28.1 mF·cm−2 at 0.1 mA·cm−2, which is much higher than the values reported for other MOF-based supercapacitors. The SASC also possessed a high energy density (3.2 μW h·cm−2) and power density (1.1 mW·cm−2), good cycling stability, and flexibility. These characteristics make our ZIF-8/PANI nanocomposite an excellent MOF-based electrode for highly flexible and lightweight energy storage applications.

The interaction between A-type interflavan bonds from cranberry proanthocyanidins (PAC) and surface virulence factors of extra-intestinal pathogenic Escherichia coli (ExPEC) was studied. Electrospun nanofibers (ESNF) were fabricated using PAC and polycaprolactone (PCL) solutions and their physical and chemical properties were characterized. The ability of PAC:PCL composite ESNF to interact with and entrap ExPEC strain 5011 (ExPEC-5011) was evaluated in vitro by plate culturing and when formulated as a biofilter and nanocoating. As a biofilter, the PAC:PCL ESNF exhibited a dose-dependent ability to entrap ExPEC-5011. Images from scanning electron and fluorescent microscopies revealed that ESNF sections with higher amounts of PAC led to higher bacterial entrapment. The effectiveness PAC:PCL ESNF to bind ExPEC when applied as a nanocoating was studied using ESNF-coated polyvinyl chloride intermittent catheter. Results indicate that ExPEC-5011 was entrapped well into the PAC:PCL ESNF coating on the catheter. Overall, our results suggest that incorporating the biomolecule PAC in ESNF is a potential means for applications requiring bacterial entrapment, such as biofunctionalization, biofiltration, and surface coating, among others.

The localized surface plasmon resonance (LSPR) effect of aggregating gold nanoparticles (AuNPs) has facilitated the development of colorimetric biosensors that can potentially be employed on site. ...

Antibiotics are widely used for improving the living conditions of livestock. However, residual antibiotics present in animal products induce several human diseases. Therefore, a simple, rapid, and cost-effective system for detecting and monitoring the presence of antibiotics in foods is in great demand to alleviate safety concerns. In this study, a highly sensitive and selective aptameric electrochemical sensing platform was designed based on nanomaterial modification and DNA nanotechnology. Electrochemically reduced graphene oxide and gold nanoparticles were used to modify the working surface of a screen-printed electrode to enhance electrical conductivity and biocompatibility. The electrode surface was further modified with self-assembled tetrahedral DNA nanostructures (TDN) to improve the detection sensitivity. The TDN allowed controlling the nano-spacing of aptamers immobilized on the electrode surface and placing aptamers in a solution-phase-like detecting environment to improve the target-binding efficiency without signal amplification modules. Differential pulse voltammetry was employed to measure electrical signals in proportion to the amount of ampicillin, the target antibiotic, present in buffer and spiked milk samples. The designed aptasensor was able to detect and measure the target ampicillin in less than 30 min over a wide concentration range of 10 pM to 1 mM, with a limit of detection of 1 pM, which is 100 times better than when using the same sensing probe without TDN modification. The aptasensor was reusable by simply rinsing with deionized water, remained stable during 15-day storage, and yielded reproducible results.

MXene is a two-dimensional (2D) nanomaterial that exhibits several superior properties suitable for fabricating biosensors. Likewise, the nucleic acid (NA) in oligomerization forms possesses highly specific biorecognition ability and other features amenable to biosensing. Hence the combined use of MXene and NA is becoming increasingly common in biosensor design and development. In this review, MXene- and NA-based biosensors are discussed in terms of their sensing mechanisms and fabrication details. MXenes are introduced from their definition and synthesis process to their characterization followed by their use in NA-mediated biosensor fabrication. The emphasis is placed on the detection of various targets relevant to agricultural and food systems, including microbial pathogens, chemical toxicants, heavy metals, organic pollutants, etc. Finally, current challenges and future perspectives are presented with an eye toward the development of advanced biosensors with improved detection performance.

Ensuring consistently high quality and safety is paramount to food producers and consumers alike. Wet chemistry and microbiological methods provide accurate results, but those methods are not conducive to rapid, onsite testing needs. Hence, many efforts have focused on rapid testing for food quality and safety, including the development of various biosensors. Herein, we focus on a group of biosensors, which provide visually recognizable colorimetric signals within minutes and can be used onsite. Although there are different ways to achieve visual color-change signals, we restrict our focus on sensors that exploit the localized surface plasmon resonance (LSPR) phenomenon of metal nanoparticles, primarily gold and silver nanoparticles. The typical approach in the design of LSPR biosensors is to conjugate biorecognition ligands on the surface of metal nanoparticles and allow the ligands to specifically recognize and bind the target analyte. This ligand-target binding reaction leads to a change in color of the test sample and a concomitant shift in the ultraviolet-visual absorption peak. Various designs applying this and other signal generation schemes are reviewed with an emphasis on those applied for evaluating factors that compromise the quality and safety of food and agricultural products. The LSPR-based colorimetric biosensing platform is a promising technology for enhancing food quality and safety. Aided by the advances in nanotechnology, this sensing technique lends itself easily for further development on field-deployable platforms such as smartphones for onsite and end-user applications.

Consumption of cranberries is associated with the putative effects of preventing urinary tract infections (UTIs). Cranberry proanthocyanidins (PAC) contain unusual double A-type linkages, which are associated with strong interactions with surface virulence factors found on UTI-causing bacteria such as extra-intestinal pathogenic Escherichia coli (ExPEC), depicting in bacterial agglutination processes. In this work, we demonstrated the efficacy of cranberry PAC (200 μg/mL) to agglutinate ExPEC (5.0 × 108 CFU/mL) in vitro as a selective interaction for the design of functionalized biosensors for potential detection of UTIs. We fabricated functionalized screen-printed electrodes (SPEs) by modifying with PAC-polyaniline (PANI) nanocomposites and tested the effectiveness of the PAC-PANI/SPE biosensor for detecting the presence of ExPEC in aqueous suspensions. Results indicated that the PAC-PANI/SPE was highly sensitive (limit of quantification of 1 CFU/mL of ExPEC), and its response was linear over the concentration range of 1–70,000 CFU/mL, suggesting cranberry PAC-functionalized biosensors are an innovative alternative for the detection and diagnosis of ExPEC-associated UTIs. The biosensor was also highly selective, reproducible, and stable.

Molecular logic gates are being applied to develop smart molecular devices for biological and biomedical applications. However, most existing molecular logic gates were constructed separately without integration, and hence their loose and jumbled structures are unfavorable to further applications. Herein, we adopt an integration design strategy to assemble three DNA probes into a DNA nanotripod and combine it with graphene oxide to build a simple and integrated platform for diverse logic operations. The assembly of multiple DNA probes and integration design produce positive synergy, which induces versatility and dramatically simplifies the construction of logic gates. Based on this simple and integrated DNA nanotripod-graphene oxide platform, a three-input majority gate, multiple elementary logic gates, and a combinatorial gate were readily realized. Further, a molecular logic computing model for the selection of composite numbers from 0 to 9 was constructed with only one DNA nanotripod and four short single-stranded DNA. Additionally, the DNA nanotripod-graphene oxide platform was able to perform logic operations steadily in a biological matrix, demonstrating its potential for use in complex environments. Due to the generality of the three DNA probes and graphene oxide used, these molecular logic gates are easy to extend for future applications, such as multi-parameter smart biosensing, stimuli-responsive cargo delivery, and intelligent diagnosis and drug release.

We recently reported a simple and cost-effective green method to produce free-standing, flexible, and highly conductive electrochemically exfoliated graphene paper (GrP) for a supercapacitor applic...

Atomic force microscopy (AFM) has recently attracted much attention due to its ability to analyze biomolecular interactions and to detect certain biomolecules, which play a crucial role in disease expression. Despite recent studies reporting AFM imaging for the analyses of biomolecules, the application of AFM-based cancer-specific biomolecule/cell detection has remained largely underexplored, especially for the early diagnosis of cancer. In this paper, we review the recent attempts, including our efforts, to analyze and detect cancer-specific biomolecules and cancer cells. We particularly focus on two AFM-based cancer diagnosis techniques: (i) AFM imaging-based biomolecular and cellular detection, (ii) AFM cantilever-based biomolecular sensing and cell analysis. It is shown that AFM-based biomolecular detection has been applied for not only early diagnosing cancer, by measuring the minute amount of cancer-specific proteins, but also monitoring of cancer progression, by correlating the amount of cancer-specific proteins with the progression of cancer. In addition, AFM-based cell imaging and detection have been employed for diagnosing cancer, by detecting cancerous cells in tissue, as well as understanding cancer progression, by characterizing the dynamics of cancer cells. This review, therefore, highlights AFM-based biomolecule/cell detection, which will pave the way for developing a fast and point-of-care diagnostic system for biomedical applications.

A facile method was developed for the fabrication of electrochemically exfoliated graphite (EG) intercalated with polyaniline (PANI) via one-step interfacial polymerization at room temperature to produce a conductive EG-PANI composite. The grafting of PANI nanoparticles on the EG surface was confirmed by microscopy and analytical tests. The EG-PANI exhibited higher areal capacitance (CA) and better electrochemical performance than either EG or PANI. A solid-state asymmetrical supercapacitor (SASc) device was fabricated to evaluate the energy-storage potential of EG-PANI using EG as negative electrode and EG-PANI as positive electrode. The SASc device exhibited high CA (80.4 ± 2.3 mF/cm2) at current density of 1 mA/cm2 and excellent capacitance retention (90.2%) after 1000 galvanostatic charge–discharge cycles at 5 mA/cm2. The specific power and energy density were as high as 4.14 mW/cm2 at current density of 5 mA/cm2 and 9.07 μWh/cm2 at current density of 1 mA/cm2, respectively. After charging just for 10 s at 3.5 V, the output of two SASc devices connected in series illuminated different forward-voltage LEDs for over 5 min without diminished brightness. This work represents a new direction for developing EG intercalated PANI to enhance capacitive efficiency of graphite materials for fabrication of supercapacitors.

Due to the widely occurring co-contamination of mycotoxins in raw food materials, simultaneous monitoring of multiple mycotoxins is needed. Herein, we report the design and fabrication of an electrochemical immunosensor for simultaneous detection of two mycotoxins, fumonisin B1 (FB1) and deoxynivalenol (DON), in a single test. A dual-channel three-electrode electrochemical sensor pattern was etched on a transparent indium tin oxide (ITO)-coated glass via photolithography and was integrated with capillary-driven polydimethylsiloxane (PDMS) microfluidic channel. The two working electrodes were functionalized with gold nanoparticles and anti-FB1 and anti-DON antibodies. Tests were performed by incubating the working electrodes in a sample solution introduced in the PDMS channel. The formation of toxin-antibody immunocomplexes on the working electrode surface produced electrochemical signal responses, which were recorded and compared with control signal to quantify individual mycotoxin concentrations. Using this dual-channel ITO-microfluidic electrochemical immunosensor we achieved limits of detection (LODs) of 97 pg/mL and 35 pg/mL, respectively for FB1 and DON, and their corresponding linear ranges of detection were 0.3–140 ppb and 0.2–60 ppb. The sensor performance, which remained stable for two weeks under proper storage, was validated by testing with ground corn extract used as a real food matrix.

We report a highly selective and sensitive electrochemical method for the detection of mobile zinc ions (Zn2+) useful for early diagnosis of prostate cancer. The working electrode on a screen-printed electrode (SPE) was modified with zincon and electrochemically exfoliated graphite complex (zincon-EG) to afford the binding of Zn2+ on zincon-EG/SPE. UV–vis and FT-IR were used to characterize zincon-EG, XRD and SEM for zincon-EG and zincon-EG-enriched with Zn2+, and cyclic voltammogram for binding of Zn2+ at zincon-EG/SPE. The optimal conditions for detecting Zn2+ were with Tris-HCl as an electrolyte (pH 7.5) over 5 min of pre-concentration and applying electrodeposition potential of −1.2 V for 100 s. Differential pulse voltammetry (DPV) was used to establish the calibration curve and the linear range of Zn2+ detection in buffer solutions as 0.25 to 1.5 mg/L. The prepared zincon-EG/SPE sensors show good repeatability (RSD = 6.9%, n = 5) and are stable for over two weeks. Three mouse serum samples derived from transgenic adenocarcinoma of mouse prostate (TRAMP) were used as real matrices for testing by after diluting (500×) and spiking with different amounts of Zn2+ (0.5, 1.0, 2.0, 3.0, 4.0 mg/L) through standard addition. From the DPV data, the original concentrations of mobile Zn2+ in the three serum samples were determined as 50, 41.5 and 5 mg/L. The average Zn2+ detection sensitivity, based on the linear responses obtained with our sensor, is 2.5 mg/L and the limit of detection is 5 μg/L.

Monodispersed cerium oxide nanoparticles (CeO2 NPs) with positive and negative surface potential were synthesized by co-precipitation method using hexamethylenetetramine (HMT) and poly(vinylpyrrolidone) (PVP), respectively, as precipitating agents. Synthesized NPs were characterized with scanning electron microscopy (SEM), UV–Visible (UV-Vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and powder X-ray diffraction (XRD). Positively charged NPs of about 30 ± 10 nm in size formed within 5 h, aggregated in number, and resulted in larger-sized NPs as a function of time. The CeO2 NPs were administered to Drosophila as a part of their diet to study the effects on the growth and development of Drosophila. While the positively charged NPs did not affect the growth of the third instar larvae, the negatively charged NPs delayed the growth of larvae by about 7 days. It required 7 more days to reach the stage of adult fly. TEM imaging of the larvae gut showed that positively charged NPs were found to be smaller, whereas the size of negatively charged NPs remained unchanged. This biodegradability could be the reason for the delayed larvae growth in the case of negatively charged particles. The distance covered by such second instar larvae fed with diet containing negatively charged CeO2 NPs was significantly lower, and their size was significantly smaller when compared to the crawling activity and size of the third instar larvae of the control group. Such positively charged NPs have high potential for use as drug delivery carriers for the treatment of disease, and negatively charged NPs may play a rather detrimental role.

A free-standing, highly flexible and conductive graphene paper (GrP) was fabricated via a simple, green, and inexpensive method. The fabrication process starts with electrochemical exfoliation of graphite as partially oxidized graphene suspension, which is then vacuum-filtered and air-dried. The procedure does not warrant any binders, toxic and corrosive agents, or high temperature. The mechanically stable GrP has excellent tensile strength of 52.3 ± 2.3 MPa at peak elongation of 5.1 ± 0.4%; ultralow sheet resistance of 2.2 Ω sq−1, which is highly stable changing by only ∼4% even after 1000 consecutive bending cycles at 10 mm bending radius; and high electrical conductivity of 3.85 × 105 S m−1. The GrP also possesses high specific capacitance of 195.8 F g−1 at 1 mV s−1 in 1 M H2SO4 as electrolyte at room temperature with Pt wire and Ag/AgCl as counter and reference electrodes, respectively. Moreover, the GrP can reusably absorb large amounts of oils and organic solvents. This environmentally friendly GrP fabrication method is of low cost and can be used for large-scale fabrication for applications such as energy-storage devices, flexible/wearable electronics, and removal of oil or toxic organic spills.

Discharge of untreated textile wastewaters loaded with dyes is not only contaminating the soil and water resources but also posing a threat to the health and socioeconomic life of the people. Hence, there is a need to devise the strategies for effective treatment of such wastewaters. The present study reports the catalytic potential of biogenic ZnO nanoparticles (ZnO NPs) synthesized by using a bacterial strain Pseudochrobactrum sp. C5 for degradation of dyes and wastewater treatment. The catalytic potential of the biogenic ZnO NPs for degradation of dyes and wastewater treatment was also compared with that of the chemically synthesized ones. The characterization of the biogenic ZnO NPs through FT-IR, XRD, and field emission scanning electron microscopy (FESEM) indicated that these are granular agglomerated particles having a size range of 90–110 nm and zeta potential of −27.41 mV. These catalytic NPs had resulted into almost complete (> 90%) decolorization of various dyes including the methanol blue and reactive black 5. These NPs also resulted into a significant reduction in COD, TDS, EC, pH, and color of two real wastewaters spiked with reactive black 5 and reactive red 120. The findings of this study suggest that the biosynthesized ZnO NPs might serve as a potential green solution for treatment of dye-loaded textile wastewaters.

We review the challenges and opportunities for biosensor research in North America aimed to accelerate translational research. We call for platform approaches based on: i) tools that can support interoperability between food, environment and agriculture, ii) open-source tools for analytics, iii) algorithms used for data and information arbitrage, and iv) use-inspired sensor design. We summarize select mobile devices and phone-based biosensors that couple analytical systems with biosensors for improving decision support. Over 100 biosensors developed by labs in North America were analyzed, including lab-based and portable devices. The results of this literature review show that nearly one quarter of the manuscripts focused on fundamental platform development or material characterization. Among the biosensors analyzed for food (post-harvest) or environmental applications, most devices were based on optical transduction (whether a lab assay or portable device). Most biosensors for agricultural applications were based on electrochemical transduction and few utilized a mobile platform. Presently, the FEAST of biosensors has produced a wealth of opportunity but faces a famine of actionable information without a platform for analytics.

Rambutan (Nephelium lappaceum) is a traditional fruit originally from Asia and now widely available in Central America. The rind of rambutan is rich in antioxidants, especially polyphenols, which have natural anti-inflammatory and antimicrobial properties. Rambutan polyphenolic extract (RPE) was encapsulated in multi-component electrospun nanofiber (ESNF) templates. These nanofibers were decorated with silver nanoparticles (AgNPs) via in situ electrochemical reduction. The RPE-loaded and AgNPs-decorated ESNF (AgNPs/RPE-ESNF) were evaluated for their hydrophilic, antioxidant, and antimicrobial properties. Results indicate that the addition of RPE to synthetic polycaprolactone (PCL) ESNF improves hydrophilicity and cell attachment and proliferation in vitro. In addition, a synergistic antibacterial and cell proliferation effect between AgNPs and RPE was observed when they were combined in the multi-functionalized ESNF system. The effectiveness of AgNPs/RPE-PCL ESNF as an antioxidant and antibacterial matrix could potentially promote wound healing and also serve as a hybrid scaffold for tissue engineering. El rambután (Nephelium lappaceum) es una fruta tradicional originaria de Asia y ahora ampliamente disponible en América Central. La corteza del rambután es rica en antioxidantes, especialmente polifenoles, que tienen propiedades antiinflamatorias y antimicrobianas naturales. El extracto polifenólico de rambután (RPE) se encapsuló en plantillas de nanofibras electrohiladas (ESNF) multicomponente. Estas nanofibras se decoraron con nanopartículas de plata (AgNP) mediante reducción electroquímica in situ. Los ESNF cargados con RPE y decorado con AgNP (AgNPs / RPE-ESNF) se evaluaron por sus propiedades hidrófilas, antioxidantes y antimicrobianas. Los resultados indican que la adición de RPE a policaprolactona sintética (PCL) ESNF mejora la hidrofilia y la unión y proliferación celular in vitro. Además, se observó un efecto sinérgico antibacteriano y de proliferación celular entre los AgNP y el RPE cuando se combinaron en el sistema ESNF multifuncionalizado. La eficacia de AgNPs / RPE-PCL ESNF como matriz antioxidante y antibacteriana podría promover la cicatrización de heridas y también servir como un andamio híbrido para la ingeniería de tejidos. Universidad Nacional, Costa Rica University of Wisconsin-Madison, United States Escuela de Química

Monodispersed colloidal gold nanoparticles (AuNPs) were synthesized by an easy, cost-effective, and eco-friendly method. The AuNPs were mostly quasi-hexagonal in shape with sizes ranging from 15 to 18 nm. A screen-printed electrode modified with AuNPs (AuNPs/SPE) was used as an electrochemical sensor for the detection of As(III) in water samples. The mechanistic details for the detection of As(III) were investigated and an electrochemical reaction mechanism was proposed. Under the optimal experimental conditions, the sensor was highly sensitive to As(III), with a limit of detection of 0.11 μg L−1 (1.51 nM), which is well below the regulatory limit of 10 μg L−1 established by the United States Environmental Protection Agency and the World Health Organization. The sensor responses were highly stable, reproducible, and linear over the As(III) concentration range of 0.075 to 30 μg L−1. The presence of co-existing heavy metal cations such as lead, copper, and mercury did not interfere with the sensor response to As(III). Furthermore, the voltammogram peaks for As(III), lead, copper, and mercury were sufficiently separate for their potential simultaneous measurement, and at very harsh acidic pH it may be possible to detect As(V). The AuNPs/SPE could detect As(III) in tap water samples at near-neutral pH, presenting potential possibilities for real-time, practical applications.

Rambutan (Nephelium lappaceum) is a traditional fruit originally from Asia and now widely available in Central America. The rind of rambutan is rich in antioxidants, especially polyphenols, which have natural anti-inflammatory and antimicrobial properties. Rambutan polyphenolic extract (RPE) was encapsulated in multicomponent electrospun nanofiber (ESNF) templates. These nanofibers were directly surface-coated with silver nanoparticles (AgNPs) via electrochemical reduction. The RPE-loaded and AgNPs-coated ESNF (AgNPs/RPE-ESNF) were evaluated for their hydrophilic, antioxidant, and antimicrobial properties. Results indicate that the addition of RPE to synthetic polycaprolactone (PCL) ESNF improves hydrophilicity and cell attachment and proliferation in vitro. In addition, a synergistic effect between AgNPs and RPE was observed when they were combined in the multi-functionalized ESNF system. The effectiveness of AgNPs/RPE-PCL ESNF as an antioxidant and antibacterial matrix could potentially promote wound healing and also serve as hybrid scaffold for tissue engineering.

Ömer Sadak; Ardahan Üniversitesi - Mühendislik Fakültesi - Elektrik-Elektronik Mühendisliği Bölümü - Elektronik Anabilim Dalı - Makale, We report the fabrication of a nanoadsorbent for the removal of heavy metals. The nanoadsorbent is comprised of ferric oxide (Fe3O4) magnetic nanoparticles (MNPs) covalently conjugated with polyacrylic acid (PAA) and further functionalized with an azo dye (Congo red, CR) using carbodiimide. This Fe3O4 core and PAA-CR Shell system (MNP/PAA-CR) exhibited binding affinity towards various cations (Pb2+, Fe2+, Fe3+, Cd2+, and Cu2+) at room temperature. Using MNP/PAA-CR we studied its heavy metal removal effectiveness and kinetics targeting Pb2+ under various reactions conditions including time and pH. The Pb2+ removal efficiency and adsorption capacity were maximal at pH 6.5 and 45 min of reaction time, and the Pb2+ adsorption kinetics better fit a pseudo second-order model than a first-order model. The adsorption of Pb2+ by MNP/PAA-CR was also investigated by the so-called Langmuir and Freundlich isotherms, and the Langmuir isotherm predicted a maximum absorption of 195.3 mg.g-1. Our results further indicated that MNP/PAA-CR is potentially reusable after desorption of the adsorbed metal with only small decline in adsorption ability over five consecutive cycles of regeneration.

Electrospun nanofibers (ESNFs) were prepared from mucilage isolated from chan and linaza beans and mozote stem commercially available in Costa Rica. Poly(vinyl alcohol) (PVA) was used as an aiding agent. Mucilage/PVA mixed solutions of different volume ratios (100:0, 80:20, 60:40, 40:60, 20:80 and 0:100) were prepared and adjusted to be similar in viscosity and electrical conductivity suitable for electrospinning. Morphology of the ESNFs was examined using scanning electron microscopy (SEM). Fourier transform infrared spectrometer (FTIR) and differential scanning calorimetry (DSC) studies were used to characterize chemical composition and thermal characteristics of the nanofibers (NFs). The ability of the NFs to support fibroblast cell proliferation was investigated in vitro using the optimized mucilage/PVA solutions. Results show plant mucilage-based ESNFs are well-suited for fibroblast cell growth, significantly better than ESNFs of PVA; and the mucilage of chan beans is better than those of mozote and linaza for supporting cell proliferation.

This work reports a highly luminescent metal-organic framework (MOF) with high surface area of 4073.9 m2 g−1, exhibiting an excellent adsorption ability and sensing performance in rapidly detecting parathion-methyl. This is an excellent example of luminescent MOFs to sensitively detect pesticides by fluorescent quenching with satisfactory results. This sensor provides a very wide linear detection range from 1.0 μg kg−1 to 10 mg kg−1, and low limit of detection 0.12 μg kg−1 (0.456 nM) for parathion-methyl. This low detection limit is much lower than the maximum residue limits (MRL) in the European Union pesticides database (0.01 mg kg−1 for fruits and vegetables, 0.02 mg kg−1 for tree nuts), as well as those of previous assays. The quenching effect of parathion-methyl is attributed to the electron-rich chemical group of nitroaromatics which might lead to photo-induced electron transfer. The fluorescent method has been reliably used for the determination of parathion-methyl in spiked irrigation water with satisfactory results, which suggests its potential for rapid detection of pesticides in food and environmental sample.

Nanocomposite of chitosan and gold nanoparticles (AuNPs) was used to develop sensors that can indicate the frozen state and thermal history of foods and other temperature-sensitive products based on the visual color change that accompanies the growth and aggregation or agglomeration of AuNPs due to their localized surface plasmon resonance. The synthesis parameters of the chitosan/AuNPs nanocomposites were optimized and the synthesis mechanisms were carefully investigated by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible spectroscopy. Optimally synthesized chitosan/AuNPs nanocomposite was used as a frozen detector, indicated by pink to dark grey color change upon freezing for one day. This sharp color change can be used to help ensure the quality of products such as seafood, meats etc. that may be affected by frozen storage. Chitosan/AuNPs nanocomposites synthesized under different set of parameters could serve as thermal history indicators (THIs) to reflect the temperature abuse of perishable foods and other temperature-sensitive biomaterials. The color of the THIs becomes more intense with the duration they suffer temperature abuse at room or higher temperature. The color change is irreversible and the THIs can be customized to fulfill different time-temperature storage requirements. These frozen detectors and THIs offer novel, cost-effective and environmentally benign alternatives to track and indicate product thermal history by visible color change, without the need of additional read-out devices. These sensors can potentially be integrated with existing packaging to help track and ensure the quality and safety of perishable food, pharmaceuticals and biomaterials.

Detection of pathogens present in food and water is essential to help ensure food safety. Among the popular methods for pathogen detection are those based on culture and colony-counting and polymerase chain reaction (PCR). However, the time-consuming nature and/or the need for sophisticated instrumentation of those methods limit their on-site applications. We have developed a rapid and highly sensitive immunosensing method for visible detection of bacteria in real matrices based on the aggregation of AuNPs without requiring any readout device. We use biotinylated anti-bacteria antibodies as bifunctional linkers (BLs) to mediate the aggregation of streptavidin-functionalized gold nanoparticles (st-AuNPs) to produce visually recognizable color change, due to surface plasmon resonance (SPR), which occurs in about 30min of total assay time when the sample is mildly agitated or within three hours in quiescent conditions. The aggregation of st-AuNPs, which produces the indication signal, is achieved very differently than in visual detection methods reported previously and hence affords ultrahigh sensitivity. While BLs can both bind to the target and crosslink st-AuNPs, their latter function is essentially disabled when they bind to the target bacteria. By varying the amount of st-AuNPs used, we can tailor the assay effectiveness improving limit of detection (LOD) down to 10CFUmL-1 of E. coli and Salmonella. Test results obtained with tap water, lake water and milk samples show that assay performance is unaffected by matrix effects. Further, in a mixture of live and autoclaved E. coli cells our assay could detect only live cells. Therefore, our BL-based immunosensor is suitable for highly sensitive, rapid, and on-site detection of bacteria in real matrices.