A home-made nanoporous gold microsensor for lead(II) detection in seawater with high sensitivity and anti-interference properties

A nanoporous gold microelectrode (NPG-μE) was fabricated and used for Pb(II) detection in seawater samples via square wave anodic stripping voltammetry (SWASV). The Au microelectrode (Au-μE) was fabricated by embedding a gold microfiber into a Pasteur pipette, and its surface was further modified by an anodization-electrochemical reduction (A-ECR) method, yielding the NPG-μE. The fabricated electrodes were characterized by cyclic voltammetry (CV) and field emission scanning electron microscopy (FE-SEM) for electrochemical and structural morphological investigations. SWASV results show a Pb(II) stripping peak at around -0.05 V vs. Ag/AgCl, sat. KCl, which is unusual for common Pb(II) detection (typically occurring at around -0.40 V) in anodic stripping voltammetry (ASV) analysis. The Pb(II) detection at less negative stripping potential is more beneficial. Hence, it exhibited anti-interference properties with Cd(II), which is attributed to the preferential deposition and stripping of the target analyte on the low-indexed crystal planes of the NPG structure. The calibration plot obtained by SWASV was linear in the concentration range of 0.1-10 μM, and the detection limit was found to be 57 nM (correlation coefficient of 0.9974). The NPG microsensor presented a 15-fold enhanced current response compared to Au-μE, with excellent sensitivity (27.2 μA μM-1 cm-2). The application of the NPG microsensor was examined by detecting Pb(II) in seawater samples, and a satisfactory performance was obtained.

Recent Advances in Bimetallic Nanoporous Gold Electrodes for Electrochemical Sensing

Bimetallic nanocomposites and nanoparticles have received tremendous interest recently because they often exhibit better properties than single-component materials. Improved electron transfer rates and the synergistic interactions between individual metals are two of the most beneficial attributes of these materials. In this review, we focus on bimetallic nanoporous gold (NPG) because of its importance in the field of electrochemical sensing coupled with the ease with which it can be made. NPG is a particularly important scaffold because of its unique properties, including biofouling resistance and ease of modification. In this review, several different methods to synthesize NPG, along with varying modification approaches are described. These include the use of ternary alloys, immersion-reduction (chemical, electrochemical, hybrid), co-electrodeposition-annealing, and under-potential deposition coupled with surface-limited redox replacement of NPG with different metal nanoparticles (e.g., Pt, Cu, Pd, Ni, Co, Fe, etc.). The review also describes the importance of fully characterizing these bimetallic nanocomposites and critically analyzing their structure, surface morphology, surface composition, and application in electrochemical sensing of chemical and biochemical species. The authors attempt to highlight the most recent and advanced techniques for designing non-enzymatic bimetallic electrochemical nanosensors. The review opens up a window for readers to obtain detailed knowledge about the formation and structure of bimetallic electrodes and their applications in electrochemical sensing.

An electrochemical microsensor based on a specific recognition element for the simultaneous detection of hydrogen peroxide and ascorbic acid in the live rat brain

A novel electrochemical microsensor was developed for the ratiometric and simultaneous determination of hydrogen peroxide (H2O2) and ascorbic acid (AA) based on the borate-phenol "switch" recognition mechanism and carbon nanotube (CNT) catalytic characteristics. First of all, a carbon fiber microelectrode (CFME) was coated with CNTs. Then, a specific probe, 9-anthraceneboronic acid pinacol ester (9-AP), was screened and decorated on CNTs through π-π stacking for the recognition of H2O2 based on the transformation of boric acid ester into electroactive phenols. CNTs not only served as the amplifiers of current signals, but also as catalysts facilitating AA oxidation. Meanwhile, ferrocenecarboxylic acid (Fc), inert to H2O2 and AA, was modified on another amino-functionalized CNT microelectrode via an amide bond as an internal reference channel for avoiding errors caused by environmental discrepancies. The two-channel ratiometric microsensor enabled the sensitive and accurate detection of H2O2 and AA simultaneously, and the detection limits were estimated to be 0.09 μM and 4.12 μM, respectively. The developed microsensor with remarkable analytical performance was finally applied for the simultaneous detection of H2O2 and AA in the live rat brain.

Potentiometric Biosensing of Ascorbic Acid, Uric Acid, and Cysteine in Microliter Volumes Using Miniaturized Nanoporous Gold Electrodes

Potentiometric redox sensing is a relatively inexpensive and passive approach to evaluate the overall redox state of complex biological and environmental solutions. The ability to make such measurements in ultra-small volumes using high surface area, nanoporous electrodes is of particular importance as such electrodes can improve the rates of electron transfer and reduce the effects of biofouling on the electrochemical signal. This work focuses on the fabrication of miniaturized nanoporous gold (NPG) electrodes with a high surface area and a small footprint for the potentiometric redox sensing of three biologically relevant redox molecules (ascorbic acid, uric acid, and cysteine) in microliter volumes. The NPG electrodes were inexpensively made by attaching a nanoporous gold leaf prepared by dealloying 12K gold in nitric acid to a modified glass capillary (1.5 mm id) and establishing an electrode connection with copper tape. The surface area of the electrodes was ~1.5 cm², providing a roughness factor of ~16 relative to the geometric area of 0.09 cm². Scanning electron microscopy confirmed the nanoporous framework. A linear dependence between the open-circuit potential (OCP) and the logarithm of concentration (e.g., Nernstian-like behavior) was obtained for all three redox molecules in 100 μL buffered solutions. As a first step towards understanding a real system, the response associated with changing the concentration of one redox species in the presence of the other two was examined. These results show that at NPG, the redox potential of a solution containing biologically relevant concentrations of ascorbic acid, uric acid, and cysteine is strongly influenced by ascorbic acid. Such information is important for the measurement of redox potentials in complex biological solutions.

Design of Stretchable Holey Gold Biosensing Electrode for Real-Time Cell Monitoring

In bioelectronics, gold thin films have been widely used as sensing electrodes for probing biological events due to their high conductivity, chemical inertness, biocompatibility, wide electrochemical window, and facile surface modification. However, they are intrinsically not stretchable, which limits their applications in detecting biological reactions when a soft biological system is mechanically deformed. Here, we report on a nanosphere lithography-based strategy to generate ordered microhole gold thin-film electrodes supported by elastomeric substrates. Both experimental and theoretical studies show that the presence of microholes substantially suppresses the catastrophic crack propagation-the main reason for electrical failure for a continuous gold film. As a result, the holey gold film achieves a ∼94% stretchable limit, after which the conductivity is lost, in contrast to ∼4% for the nonstructured counterpart. Furthermore, the pinhole gold electrode is successfully used to monitor the H₂O₂ released from living cells under dynamic stretching conditions.

Electrochemical Detection of H2O2 Released from Prostate Cancer Cells Using Pt Nanoparticle-Decorated rGO–CNT Nanocomposite-Modified Screen-Printed Carbon Electrodes

In this study, we fabricated platinum nanoparticles (PtNP)-decorated, porous reduced graphene oxide (rGO)–carbon nanotube (CNT) nanocomposites on a PtNP-deposited screen-printed carbon electrode (PtNP/rGO–CNT/PtNP/SPCE) for detection of hydrogen peroxide (H2O2), which is released from prostate cancer cells LNCaP. The PtNP/rGO–CNT/PtNP/SPCE was fabricated by a simple electrochemical deposition and co-reduction method. In addition, the amperometric response of the PtNP/rGO–CNT/PtNP/SPCE electrode was evaluated through consecutive additions of H2O2 at an applied potential of 0.2 V (vs. Ag pseudo-reference electrode). As a result, the prepared PtNP/rGO–CNT/PtNP/SPCE showed good electrocatalytic activity toward H2O2 compared to bare SPCE, rGO–CNT/SPCE, PtNP/SPCE, and rGO–CNT/PtNP/SPCE. In addition, the PtNP/rGO–CNT/PtNP/SPCE electrode exhibited a sensitivity of 206 μA mM−1·cm−2 to H2O2 in a linear range of 25 to 1000 μM (R2 = 0.99). Moreover, the PtNP/rGO–CNT/PtNP/SPCE electrode was less sensitive to common interfering substances, such as ascorbic acid, uric acid, and glucose than H2O2. Finally, real-time monitoring of H2O2 released from LNCaP cells was successfully performed by this electrode. Therefore, we expect that the PtNP/rGO–CNT/PtNP/SPCE can be utilized as a promising electrochemical sensor for practical nonenzymatic detection of H2O2 in live cells or clinical analysis.

MoS2/Pt nanocomposite-functionalized microneedle for real-time monitoring of hydrogen peroxide release from living cells

This work describes the adaptive use of a conventional stainless steel acupuncture needle as the electrode substrate for construction of a molybdenum disulfide (MoS₂) and platinum nanoparticles (PtNPs) layer-modified microneedle sensor for real-time monitoring of hydrogen peroxide (H₂O₂) release from living cells. To construct the nanocomposite-functionalized microneedle, the needle surface was first coated with a gold film by ion sputtering to enhance the conductivity. Subsequently, an electrochemical deposition method was successfully employed to deposit MoS₂ nanosheet and Pt nanoparticles on the needle tip as the sensing interface. Electrochemical study demonstrated that the MoS₂/PtNPs nanocomposite-modified needle exhibited excellent catalytic performance and low over-potential toward the reduction of H₂O₂. Not only did the microneedle achieve a wide linear range from 1 to 100 μmol L^-1 with a limit of detection down to 0.686 μmol L^-1, but it also realized the highly specific detection of H₂O₂. Owing to these remarkable analytical advantages, the prepared microneedle was applied to determine H₂O₂ release from living cells with satisfactory results. The MoS₂/PtNPs nanocomposite-functionalized microneedle sensor is simple and affordable, and can serve as a promising electrochemical nonenzymatic sensing platform. Moreover, this superfine needle sensor shows great potential for real-time monitoring of reactive oxygen species in vivo with minimal damage.

Nanoparticles as Theranostic Vehicles in Experimental and Clinical Applications-Focus on Prostate and Breast Cancer

Prostate and breast cancer are the second most and most commonly diagnosed cancer in men and women worldwide, respectively. The American Cancer Society estimates that during 2016 in the USA around 430,000 individuals were diagnosed with one of these two types of cancers, and approximately 15% of them will die from the disease. In Europe, the rate of incidences and deaths are similar to those in the USA. Several different more or less successful diagnostic and therapeutic approaches have been developed and evaluated in order to tackle this issue and thereby decrease the death rates. By using nanoparticles as vehicles carrying both diagnostic and therapeutic molecular entities, individualized targeted theranostic nanomedicine has emerged as a promising option to increase the sensitivity and the specificity during diagnosis, as well as the likelihood of survival or prolonged survival after therapy. This article presents and discusses important and promising different kinds of nanoparticles, as well as imaging and therapy options, suitable for theranostic applications. The presentation of different nanoparticles and theranostic applications is quite general, but there is a special focus on prostate cancer. Some references and aspects regarding breast cancer are however also presented and discussed. Finally, the prostate cancer case is presented in more detail regarding diagnosis, staging, recurrence, metastases, and treatment options available today, followed by possible ways to move forward applying theranostics for both prostate and breast cancer based on promising experiments performed until today.

Zooming In on Plant Hormone Analysis: Tissue- and Cell-Specific Approaches

Plant hormones are a group of naturally occurring, low-abundance organic compounds that influence physiological processes in plants. Our knowledge of the distribution profiles of phytohormones in plant organs, tissues, and cells is still incomplete, but advances in mass spectrometry have enabled significant progress in tissue- and cell-type-specific analyses of phytohormones over the last decade. Mass spectrometry is able to simultaneously identify and quantify hormones and their related substances. Biosensors, on the other hand, offer continuous monitoring; can visualize local distributions and real-time quantification; and, in the case of genetically encoded biosensors, are noninvasive. Thus, biosensors offer additional, complementary technologies for determining temporal and spatial changes in phytohormone concentrations. In this review, we focus on recent advances in mass spectrometry-based quantification, describe monitoring systems based on biosensors, and discuss validations of the various methods before looking ahead at future developments for both approaches.

Nanoporous-Gold-Based Electrode Morphology Libraries for Investigating Structure-Property Relationships in Nucleic Acid Based Electrochemical Biosensors

Nanoporous gold (np-Au) electrode coatings significantly enhance the performance of electrochemical nucleic acid biosensors because of their three-dimensional nanoscale network, high electrical conductivity, facile surface functionalization, and biocompatibility. Contrary to planar electrodes, the np-Au electrodes also exhibit sensitive detection in the presence of common biofouling media due to their porous structure. However, the pore size of the nanomatrix plays a critical role in dictating the extent of biomolecular capture and transport. Small pores perform better in the case of target detection in complex samples by filtering out the large nonspecific proteins. On the other hand, larger pores increase the accessibility of target nucleic acids in the nanoporous structure, enhancing the detection limits of the sensor at the expense of more interference from biofouling molecules. Here, we report a microfabricated np-Au multiple electrode array that displays a range of electrode morphologies on the same chip for identifying feature sizes that reduce the nonspecific adsorption of proteins but facilitate the permeation of target DNA molecules into the pores. We demonstrate the utility of the electrode morphology library in studying DNA functionalization and target detection in complex biological media with a special emphasis on revealing ranges of electrode morphologies that mutually enhance the limit of detection and biofouling resilience. We expect this technique to assist in the development of high-performance biosensors for point-of-care diagnostics and facilitate studies on the electrode structure-property relationships in potential applications ranging from neural electrodes to catalysts.

Fabrication of single Pt@Au nanowire electrodes for monitoring hydrogen peroxide released from living cells

Single Pt@AuNWEs were fabricated by a Cu UPD/Pt redox replacement technique, and were applied to monitoring H₂O₂ released from living cells.

MoS2 nanosheet–Au nanorod hybrids for highly sensitive amperometric detection of H2O2 in living cells

MoS₂–Au hybrids were utilized to construct a sensitive H₂O₂ electrochemical biosensor for the determination of H₂O₂ released from living cells.

Pd Nanoparticles Decorated N-Doped Graphene Quantum Dots@N-Doped Carbon Hollow Nanospheres with High Electrochemical Sensing Performance in Cancer Detection

The development of carbon based hollow-structured nanospheres (HNSs) materials has stimulated growing interest due to their controllable structure, high specific surface area, large void space, enhanced mass transport, and good biocompatibility. The incorporation of functional nanomaterials into their core and/or shell opens new horizons in designing functionalized HNSs for a wider spectrum of promising applications. In this work, we report a new type of functionalized HNSs based on Pd nanoparticles (NPs) decorated double shell structured N-doped graphene quantum dots (NGQDs)@N-doped carbon (NC) HNSs, with ultrafine Pd NPs and "nanozyme" NGQDs as dual signal-amplifying nanoprobes, and explore their promising application as a highly efficient electrocatalyst in electrochemical sensing of a newly emerging biomarker, i.e., hydrogen peroxide (H2O2), for cancer detection. Due to the synergistic effect of the robust and conductive HNS supports and catalytically active Pd NPs and NGQD in facilitating electron transfer, the NGQD@NC@Pd HNS hybrid material exhibits high electrocatalytic activity toward the direct reduction of H2O2 and can promote the electrochemical reduction reaction of H2O2 at a favorable potential of 0 V, which effectively restrains the redox of most electroactive species in physiological samples and eliminates interference signals. The resultant electrochemical H2O2 biosensor based hybrid HNSs materials demonstrates attractive performance, including low detection limit down to nanomole level, short response time within 2 s, as well as high sensitivity, reproducibility, selectivity, and stability, and have been used in real-time tracking of trace amounts of H2O2 secreted from different living cancer cells in a normal state and treated with chemotherapy and radiotherapy.

Decoration of GO with Fe spinel-Naf/DMAP: an electrochemical probe for sensing H2O2 reduction

We herein report the preparation of graphene oxide decorated with Fe spinel (Fe₃O₄)-Naf/DMAP for an unprecedented and highly selective non-enzymatic electrochemical sensing of hydrogen peroxide.

A facile electrochemical approach to fabricate a nanoporous gold film electrode and its electrocatalytic activity towards dissolved oxygen reduction

NPGF electrode was fabricated in absence of alloys, templates & chemical reducing agents and its electrocatalytic activity towards DO reduction was achieved at very low overpotential with enhanced sensitivity.