Gonca Bulbul

Portable Nanoparticle-Based Sensors for Food Safety Assessment

The use of nanotechnology-derived products in the development of sensors and analytical measurement methodologies has increased significantly over the past decade. Nano-based sensing approaches include the use of nanoparticles (NPs) and nanostructures to enhance sensitivity and selectivity, design new detection schemes, improve sample preparation and increase portability. This review summarizes recent advancements in the design and development of NP-based sensors for assessing food safety. The most common types of NPs used to fabricate sensors for detection of food contaminants are discussed. Selected examples of NP-based detection schemes with colorimetric and electrochemical detection are provided with focus on sensors for the detection of chemical and biological contaminants including pesticides, heavy metals, bacterial pathogens and natural toxins. Current trends in the development of low-cost portable NP-based technology for rapid assessment of food safety as well as challenges for practical implementation and future research directions are discussed.

Probing phosphatase activity using redox active nanoparticles: a novel colorimetric approach for the detection of enzyme activity.

A new colorimetric assay for the detection of alkaline phosphatase (ALP) activity is reported based on the surface reactivity and optical properties of redox active nanoparticles of cerium oxide, or nanoceria. The method takes advantage of nanoceria color changes after interaction with products of the ALP catalyzed reaction, resulting in charge transfer complexes with very strong absorption characteristics. The developed assay is easy-to-use, robust and cost effective and does not involve labeled reagents, secondary enzymes or soluble dyes. Hydrolytic products of more stable substrates (catechol monophosphate, ascorbic 2-phosphate and hydroquinone diphosphate) that could previously not be used in ALP assays can be conveniently colorimetrically detected with this assay. A detection limit of 0.04 U/L ALP with a linear range up to 2U/L was obtained with ascorbic 2-phosphate substrate. The proposed assay can eliminate multistep procedures and minimize problems associated with the poor stability of substrates and enzyme labels of conventional ALP assays. The assay has been adapted to a paper platform and has demonstrated functionality for ALP detection in human serum. This sensing concept can find wide applications as a general approach for improving sensitivity and simplifying detection schemes of colorimetric bioassays, e.g. enzyme, gene, immuno and aptamer assays and related affinity sensing methods.

Evaluation of the oxidase like activity of nanoceria and its application in colorimetric assays.

Nanomaterial-based enzyme mimics have attracted considerable interest in chemical analysis as alternative catalysts to natural enzymes. However, the conditions in which such particles can replace biological catalysts and their selectivity and reactivity profiles are not well defined. This work explored the oxidase like properties of nanoceria particles in the development of colorimetric assays for the detection of dopamine and catechol. Selectivity of the system with respect to several phenolic compounds, the effect of interferences and real sample analysis are discussed. The conditions of use such as buffer composition, selectivity, pH, reaction time and particle type are defined. Detection limits of 1.5 and 0.2μM were obtained with nanoceria for dopamine and catechol. The same assay could be used as a general sensing platform for the detection of other phenolics. However, the sensitivity of the method varies significantly with the particle type, buffer composition, pH and with the structure of the phenolic compound. The results demonstrate that nanoceria particles can be used for the development of cost effective and sensitive methods for the detection of these compounds. However, the selection of the particle system and experimental conditions is critical for achieving high sensitivity. Recommendations are provided on the selection of the particle system and reaction conditions to maximize the oxidase like activity of nanoceria.

Applications and implications of nanoceria reactivity: measurement tools and environmental impact

Cerium oxide nanoparticles or nanoceria have a unique structure and interesting and unusual redox and catalytic properties that vary with the size, shape, charge, surface coating and chemical reactivity. This paper highlights applications and environmental implications of nanoceria, and describes methodologies for the assessment of the reactivity and potential toxicological effects of these particles. The physical and chemical properties in the particle design that are responsible for their reactivity and transformation in environmental and biological conditions are described. Processes such as surface oxidation, formation of surface complexes and potential interaction with redox active components of the environment are discussed. An overview of analytical characterization methods for study of nanoceria properties, reactivity and impact, highlighting methodological challenges and limitations is presented. Examples discussed include strategies to determine physicochemical properties, cytotoxicity and antioxidant or pro-oxidant activity in various exposure environments. Development of new measurement tools to facilitate rapid assessment and accelerate screening of these particles for their reactivity and effects is discussed. Future research needs for environmental assessment of benefits and potential risks associated with the use of nanoceria are also provided.

Redox reactivity of cerium oxide nanoparticles against dopamine

The interaction between dopamine and the redox active cerium oxide nanoparticles, or nanoceria was studied using a suite of spectroscopic and surface characterization methods. Changes in the chemical reactivity and concentration of dopamine upon exposure to nanoceria was assessed in aqueous solutions and a human physiological fluid--human serum. The results indicate strong attachment of dopamine to the nanoparticle surface through oxidation followed by chemisorption of the oxidative product with formation of a charge transfer complex. Such oxidation/surface adsorption processes between nanoceria and dopamine lead to a reduction of the concentration of free dopamine in aqueous environments. These findings suggest that the redox reactivity of nanoceria may alter dopamine levels in biological systems exposed to these particles and indicate the need for a comprehensive assessment of the potential neurological consequences that might result from intended or unintended exposure to these particles.

ssDNA‐Functionalized Nanoceria: A Redox‐Active Aptaswitch for Biomolecular Recognition

Quantification of biomolecular binding events is a critical step for the development of biorecognition assays for diagnostics and therapeutic applications. This paper reports the design of redox-active switches based on aptamer conjugated nanoceria for detection and quantification of biomolecular recognition. It is shown that the conformational transition state of the aptamer on nanoceria, combined with the redox properties of these particles can be used to create surface based structure switchable aptasensing platforms. Changes in the redox properties at the nanoceria surface upon binding of the ssDNA and its target analyte enables rapid and highly sensitive measurement of biomolecular interactions. This concept is demonstrated as a general applicable method to the colorimetric detection of DNA binding events. An example of a nanoceria aptaswitch for the colorimetric sensing of Ochratoxin A (OTA) and applicability to other targets is provided. The system can sensitively and selectivity detect as low as 0.15 × 10(-9) m OTA. This novel assay is simple in design and does not involve oligonucleotide labeling or elaborate nanoparticle modification steps. The proposed mechanism discovered here opens up a new way of designing optical sensing methods based on aptamer recognition. This approach can be broadly applicable to many bimolecular recognition processes and related applications.

Nano-Aptasensing in Mycotoxin Analysis: Recent Updates and Progress

Recent years have witnessed an overwhelming integration of nanomaterials in the fabrication of biosensors. Nanomaterials have been incorporated with the objective to achieve better analytical figures of merit in terms of limit of detection, linear range, assays stability, low production cost, etc. Nanomaterials can act as immobilization support, signal amplifier, mediator and artificial enzyme label in the construction of aptasensors. We aim in this work to review the recent progress in mycotoxin analysis. This review emphasizes on the function of the different nanomaterials in aptasensors architecture. We subsequently relate their features to the analytical performance of the given aptasensor towards mycotoxins monitoring. In the same context, a critically analysis and level of success for each nano-aptasensing design will be discussed. Finally, current challenges in nano-aptasensing design for mycotoxin analysis will be highlighted.

DNA assay based on Nanoceria as Fluorescence Quenchers (NanoCeracQ DNA assay)

Functional nanomaterials with fluorescent or quenching abilities are important for the development of molecular probes for detection and studies of nucleic acids. Here, we describe a new class of molecular nanoprobes, the NanoCeracQ that uses nanoceria particles as a nanoquencher of fluorescent oligonucleotides for rapid and sensitive detection of DNA sequences and hybridization events. We show that nanoceria forms stable and reversible bionanoconjugates with oligonucleotides and can specifically recognize and detect DNA sequences in a single step. In absence of the target DNA, the nanoprobe produced minimal background fluorescence due to the high quenching efficiency of nanoceria. Competitive binding of the target induced a concentration dependent increase in the fluorescence signal due to hybridization and release of the fluorescent tag from the nanoparticle surface. The nanoprobe enabled sensitive detection of the complementary strand with a detection limit of 0.12 nM, using a single step procedure. The results show that biofunctionalized nanoceria can be used as a universal nanoquencher and nanosensing platform for fluorescent DNA detection and studies of nucleic acid interactions. This approach can find broad applications in molecular diagnostics, sensor development, gene expression profiling, imaging and forensic analysis.

Reactivity of nanoceria particles exposed to biologically relevant catechol-containing molecules

The interaction of nanoceria particles with catechol-like molecules of physiological importance, including dopamine, norepinephrine, epinephrine, serotonin, 3,4 dihydroxyphenylaceticacid (DOPAC) and L-3-(3,4-dihydroxyphenylalanine) (L-DOPA) was studied to obtain predictive information of their behavior in biological systems. A suite of complementary techniques including UV-Vis spectroscopy, electrochemistry, dynamic light scattering (DLS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) demonstrated alteration in the spectral, redox and surface properties of nanoceria exposed to these molecules in an aqueous environment. Binding of catechol to the surface of nanoceria diminished the oxidase-like activity of these particles against an organic dye, TMB (3,3,5,5-tetramethylbenzedine), but enhanced their ability to react with and inactivate reactive oxygen species. Therefore, the reactivity of these particles can be modulated by addition of catechol-like molecules. These findings can help develop predictive models of the behavior and potential effects of nanoceria particles in complex environments.

Nanopipettes as Monitoring Probes for the Single Living Cell: State of the Art and Future Directions in Molecular Biology

Examining the behavior of a single cell within its natural environment is valuable for understanding both the biological processes that control the function of cells and how injury or disease lead to pathological change of their function. Single-cell analysis can reveal information regarding the causes of genetic changes, and it can contribute to studies on the molecular basis of cell transformation and proliferation. By contrast, whole tissue biopsies can only yield information on a statistical average of several processes occurring in a population of different cells. Electrowetting within a nanopipette provides a nanobiopsy platform for the extraction of cellular material from single living cells. Additionally, functionalized nanopipette sensing probes can differentiate analytes based on their size, shape or charge density, making the technology uniquely suited to sensing changes in single-cell dynamics. In this review, we highlight the potential of nanopipette technology as a non-destructive analytical tool to monitor single living cells, with particular attention to integration into applications in molecular biology.