Improvement of the electrochemical and electrocatalytic behavior of Prussian blue/carbon nanotubes composite via ionic liquid treatment

A screen-printed microelectrode for detection of hydrogen peroxide in solid tumor in vivo

Hydrogen peroxide (H2O2), a crucial redox signaling molecule and neuromodulator, is closely associated with pathological processes, including cancer progression and neurodegenerative disorders. Current methods for in vivo H2O2 detection, such as fluorescence imaging and chemiluminescence, suffer from the limitation of spatial resolution and invasiveness, which makes it difficult to monitor oxidative stress gradients in deep-seated tumors. Therefore, this research developed an implantable triple-electrode biosensor fabricated via screen-printing technology based on carboxylated multi-walled carbon nanotubes (MWCNT) and Prussian blue (PB) nanocomposites. The biosensor presented dual linear detection ranges of 0.8-1126 μM (R2 = 0.9937) and 1286-3766 μM (R2 = 0.9939) with a 0.47 μM detection limit. It demonstrated a >95 % specificity compared with other interfering substances and maintained 93.2 % signal retention over 30 days. Particularly, in situ implantation in melanoma-bearing mice with one-week-growth-time solid tumors revealed the H2O2 levels 12- to 18-fold higher than in normal tissues, consistent with cancer-associated oxidative stress mechanisms. This platform addresses challenges such as rapid enzymatic degradation and microenvironmental complexity, enabling invasive profiling of H2O2 detection in solid tumors.

Bimetallic MOF synergy molecularly imprinted ratiometric electrochemical sensor based on MXene decorated with polythionine for ultra-sensitive sensing of catechol

Dual-signal ratiometric molecularly imprinted polymer (MIP) electrochemical sensors with bimetallic active sites and high-efficiency catalytic activity were fabricated for the sensing of catechol (CC) with high selectivity and sensitivity. The amino-functionalization bimetallic organic framework materials (Fe@Ti-MOF-NH₂), coupled with two-dimensional layered titanium carbide (MXene) co-modified glassy carbon electrode provides an expanded surface while amplifying the output signal through the electropolymerization immobilization of polythionine (pTHi) and MIP. The oxidation of CC and pTHi were presented as the response signal and the internal reference signal. The oxidation peak current at +0.42 V rose with increased concentration of CC, while the peak currents of pTHi at -0.20 V remained constant. Compared to the common single-signal sensing system, this one (MIP/pTHi/MXene/Fe@Ti-MOF-NH₂/GCE), a novel ratiometric MIP electrochemical sensor exhibited two segments wide dynamic range of 1.0-300 μM (R² = 0.9924) and 300-4000 μM (R² = 0.9912), as well as an ultralow detection limit of 0.54 μM (S/N = 3). Due to the specific recognition function of MIPs and the advantages of built-in correction of pTHi, the prepared surface imprinting sensor presented an excellent performance in selectivity and reproducibility. Besides, this sensor possessed superior anti-interference ability with ions and biomolecules, excellent reproducibility, repeatability, and acceptable stability. Furthermore, the proposed sensing system exhibits high specific recognition in the determination of environmental matrices and biological fluids in real samples with satisfactory results. Therefore, this signal-enhanced ratiometric MIP electrochemical sensing strategy can accurately and selectively analyze and detect other substances.

Determining the depth of surface charging layer of single Prussian blue nanoparticles with pseudocapacitive behaviors

Understanding the hybrid charge-storage mechanisms of pseudocapacitive nanomaterials holds promising keys to further improve the performance of energy storage devices. Based on the dependence of the light scattering intensity of single Prussian blue nanoparticles (PBNPs) on their oxidation state during sinusoidal potential modulation at varying frequencies, we present an electro-optical microscopic imaging approach to optically acquire the Faradaic electrochemical impedance spectroscopy (oEIS) of single PBNPs. Here we reveal typical pseudocapacitive behavior with hybrid charge-storage mechanisms depending on the modulation frequency. In the low-frequency range, the optical amplitude is inversely proportional to the square root of the frequency (∆I ∝ f^−0.5; diffusion-limited process), while in the high-frequency range, it is inversely proportional to the frequency (∆I ∝ f⁻¹; surface charging process). Because the geometry of single cuboid-shaped PBNPs can be precisely determined by scanning electron microscopy and atomic force microscopy, oEIS of single PBNPs allows the determination of the depth of the surface charging layer, revealing it to be ~2 unit cells regardless of the nanoparticle size.

The surface charging layer in nanomaterials, which determines their pseudocapacitive behavior, is challenging to characterize. Here the authors perform Faradic electrochemical impedance spectroscopy measurements of single cuboid Prussian blue nanoparticles, displaying a hybrid charge storage mechanism, and determine the depth of the surface charging layer.

A novel label-free electrochemical immunesensor for ultrasensitive detection of LT toxin using prussian blue@gold nanoparticles composite as a signal amplification

In the current study, a novel electrochemical label-free immunosensor is proposed for sensitive detection of heat-labile enterotoxin (LT) from Escherichia coli. Firstly, a glassy carbon electrode (GCE) was modified by a mixture containing reduced graphene oxide/room temperature ionic liquid (rGO/RTIL) composite. Then, simultaneous electrodeposition of prussian blue and gold nanoparticles led to formation of prussian blue@gold nanoparticles (PB@GNPs) composite on the electrode surface. The modified electrode was characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. After immobilization of anti-LT and blocking the unreacted sites with BSA (bovine serum albumin), the analytical performance of the proposed immunosensor was evaluated under optimal conditions (i.e. optimal pH, incubation time and temperature of incubation). Square wave voltammetry (SWV) was used to determine different concentrations of the LT antigen. The linear dynamic range of the proposed immunosensor was from 0.01 to 50 µg/mL and the detection limit of the immunosensor was found to be 0.0023 µg/mL. An acceptable selectivity in the real sample, long-term stability and goodreproducibility made the fabricated immunosensor a good candidate for detecting LT.

Reasonable design of an MXene-based enzyme-free amperometric sensing interface for highly sensitive hydrogen peroxide detection

Sensitive detection of H₂O₂ in the nano- to micromolar range is critical for health monitoring and disease diagnosis. Two-dimensional transition metal carbides or/and nitrides (called MXenes, MXs) have excellent potential applications in the electrochemical field due to their outstanding electrical conductivity and catalytic properties. In this work, Ti₃C₂T_x (MX) was employed for the construction of a sensitive and enzyme-free electrochemical sensing interface for the detection of hydrogen peroxide (H₂O₂) through a simple and effective method. Prussian blue (PB) was electrochemically deposited on the surface of a glassy carbon electrode (GCE). Chitosan (CS) and MX were sequentially dripped onto the PB modified GCE surface. The reasonable fabrication of the MX/CS/PB/GCE sensing interface presented good electrochemical sensing performance towards H₂O₂ with a low limit of detection (4 nM), a wide linear range from 50 nM to 667 μM and good selectivity. The proposed MX/CS/PB/GCE has been proven to monitor H₂O₂ in food samples and biological samples with recoveries between 94.7% and 100.3%. This work has made a beneficial attempt and research for exploring and expanding the application of MXs in the field of electrochemical sensing.

Accessing the Electrochemical Activity of Single Nanoparticles by Eliminating the Heterogeneous Electrical Contacts

While single nanoparticle electrochemistry holds great promise for establishing the structure-activity relationship (SAR) of electroactive nanomaterials, as it removes the heterogeneity among individuals, successful SAR studies remain rare. When one nanoparticle is seen to exhibit better performance than the others, it is often simply attributed to better activity of the particular individual. By taking the ion insertion reaction of Prussian blue nanoparticles as an example, here we show that the electrical contact between nanoparticles and electrode, a previously overlooked factor, was greatly distinct from one nanoparticle to another and significantly contributed to the apparent heterogeneity in the reactivity and cyclability. An individual nanoparticle with intrinsically perfect structure (size, facet, crystallinity, and so on) could be completely inactive, simply due to poor electrical contacts, which blurred the SAR and likely caused failures. We further proposed a sputter-coating method to enhance the electrical contacts by depositing an ultrathin platinum layer onto the sample. Such an approach was routinely adopted in scanning electron microscopy to improve the electron mobility between nanoparticles and substrate. Elimination of heterogeneous contacts ensured that the electrochemical activity of single nanoparticles can be accessed and further correlated with their structural features, thus paving the way for single nanoparticle electrochemistry to deliver on its promises in SAR.

Thin-Film Electrochemistry of Single Prussian Blue Nanoparticles Revealed by Surface Plasmon Resonance Microscopy

Electrochemical behaviors of Prussian blue (PB) have been intensively studied for decades because it not only serves as a model electro-active nanomaterial in fundamental electrochemistry but also a promising metal-ion storage electrode material for developing rechargeable batteries. Traditional electrochemical studies are mostly based on bulk materials, leading to an averaged property of billions of PB nanoparticles. In the present work, we employed surface plasmon resonance microscopy (SPRM) to resolve the optical cyclic voltammograms of single PB nanoparticles during electrochemical cycling. It was found that the electrochemical behavior of single PB nanoparticles nicely followed a classical thin-film electrochemistry theory. While kinetic controlled electron transfer was observed at slower scan rates, intraparticle diffusion of K⁺ ions began to take effect when the scan rate was higher than 60 mV/s. We further found that the electrochemical activity among individual PB nanoparticles was very heterogeneous and such a phenomenon has not been previously observed in the bulk measurements. The present work not only demonstrates the thin-film electrochemical feature of single electro-active nanomaterials for the first time, it also validates the applicability of SPRM technique to investigate a variety of metal ion-storage battery materials, with implications in both fundamental nanoelectrochemistry and electro-active materials for sensing and battery applications.

Facile synthesis of Prussian blue nanocubes/silver nanowires network as a water-based ink for the direct screen-printed flexible biosensor chips

The large-scale fabrication of nanocomposite based biosensors is always a challenge in the technology commercialization from laboratory to industry. In order to address this issue, we have designed a facile chemical method of fabricated nanocomposite ink applied to the screen-printed biosensor chip. This ink can be derived in the water through the in-situ growth of Prussian blue nanocubes (PBNCs) on the silver nanowires (AgNWs) to construct a composite nanostructure by a facile chemical method. Then a miniature flexible biosensor chip was screen-printed by using the prepared nanocomposite ink. Due to the synergic effects of the large specific surface area, high conductivity and electrocatalytic activity from AgNWs and PBNCs, the as-prepared biosensor chip exhibited a fast response (<3s)， a wider linear response from 0.01 to 1.3mM with an ultralow LOD=5µm, and the ultrahigh sensitivities of 131.31 and 481.20µAmM^-1cm^-2 for the detections of glucose and hydrogen peroxide (H₂O₂), respectively. Furthermore, the biosensor chip exhibited excellent stability, good reproducibility and high anti-interference ability towards physiological substances under a very low working potential of -0.05. Hence, the proposed biosensor chip also showed a promising potential for the application in practical analysis.

Electrocodeposition of silver and silicomolybdate hybrid nanocomposite for nonenzymatic hydrogen peroxide sensor

Electrocodeposition of silver and silicomolybdate hybrid nanocomposite using negatively charged silicomolybdate to induce silver ions to co-deposit on electrode surface.

A ternary nanocomposite electrode of polyoxometalate/carbon nanotubes/gold nanoparticles for electrochemical detection of hydrogen peroxide

In this work, a nanocomposite film electrode containing polyoxometalate (POM) clusters K₆P₂W₁₈O₆₂ (P₂W₁₈), carbon nanotubes (CNTs) and Au nanoparticles (AuNPs) was fabricated by a layer-by-layer self-assembly technique.