Sodium alginate nanocomposite based efficient system for the removal of organic and inorganic pollutants from wastewater.

An effective and selective catalytic system based on cerium oxide-stannous oxide (CeO2-SnO) wrapped Na-alginate hydrogel was developed for the selective reduction of potassium ferricyanide (K3[Fe(CN)6]). Na-alginate hydrogel was used as a reacting container for CeO2-SnO nanoparticles. Na-alginate wrapped CeO2-SnO (Alg/CeO2-SnO) was applied as a catalyst and examined toward the reduction of several hazardous pollutants, such as nitrophenols, dyes and K3[Fe(CN)6]. Alg/CeO2-SnO nanocatalyst was mostly selective toward K3[Fe(CN)6] since it was more effective and economical for reduction of K3[Fe(CN)6]. Further different parameters like catalyst amount, reducing agent amount, K3[Fe(CN)6] concentration and recyclability were optimized. The increase in both nanocatalyst amount and NaBH4 concentration resulted in increasing the rate of the catalytic reduction of K3[Fe(CN)6]. Alg/CeO2-SnO nanocatalyst reduced K3[Fe(CN)6] in 4.0 min with a reaction rate constant of 0.9114 min-1. The nanocatalyst can be easily recovered by pulling the hydrogel from the reaction medium up to four cycles. Alg/CeO2-SnO nanocatalyst was also examined in real samples like irrigation water, sea water, well water, university water, which was effective for K3[Fe(CN)6] reduction by 95.16%-96.54%. This novel approach provides a new catalyst for efficient removal of K3[Fe(CN)6] from real samples and can be a time and cost alternative tool for environmental safety.

Reactive oxygen species scavenging and inflammation mitigation enabled by biomimetic prussian blue analogues boycott atherosclerosis.

BACKGROUND: As one typical cardiovascular disease, atherosclerosis severely endanger people' life and cause burden to people health and mentality. It has been extensively accepted that oxidative stress and inflammation closely correlate with the evolution of atherosclerotic plaques, and they directly participate in all stages of atherosclerosis. Regarding this, anti-oxidation or anti-inflammation drugs were developed to enable anti-oxidative therapy and anti-inflammation therapy against atherosclerosis. However, current drugs failed to meet clinical demands. METHODS: Nanomedicine and nanotechnology hold great potential in addressing the issue. In this report, we engineered a simvastatin (Sim)-loaded theranostic agent based on porous manganese-substituted prussian blue (PMPB) analogues. The biomimetic PMPB carrier could scavenge ROS and mitigate inflammation in vitro and in vivo. Especially after combining with Sim, the composite Sim@PMPB NC was expected to regulate the processes of atherosclerosis. As well, Mn2+ release from PMPB was expected to enhance MRI. RESULTS: The composite Sim@PMPB NC performed the best in regulating the hallmarks of atherosclerosis with above twofold decreases, typically such as oxidative stress, macrophage infiltration, plaque density, LDL internalization, fibrous cap thickness and foam cell birth, etc. Moreover, H2O2-induced Mn2+ release from PMPB NC in atherosclerotic inflammation could enhance MRI for visualizing plaques. Moreover, Sim@PMPB exhibited high biocompatibility according to references and experimental results. CONCLUSIONS: The biomimetic Sim@PMPB theranostic agent successfully stabilized atherosclerotic plaques and alleviated atherosclerosis, and also localized and magnified atherosclerosis, which enabled the monitoring of H2O2-associated atherosclerosis evolution after treatment. As well, Sim@PMPB was biocompatible, thus holding great potential in clinical translation for treating atherosclerosis.

A sensitive spectrofluorimetry method based on S and N dual-doped carbon nanoparticles for ultra-trace detection of ferrocyanide ion in food salt samples.

An ultra-sensitive spectrofluorimetry method was developed and validated for the rapid determination of ferrocyanide ions (hexacyanidoferrate(II), FeCN6 4-, FCNs) by using sulphur (S) and nitrogen (N) dual-doped fluorescence carbon nanoparticles (S,N-FCNPs) as nanoprobe. The fluorescence of S,N-FCNPs was strongly reduced due to the dynamic interaction between S,N-FCNPs and FeCNs. The developed method proved to be highly sensitive and selective for FeCNs detection with linearity in three concentration ranges over four orders of magnitude, covering 0.01-200.0 µg/mL. A limit of detection (LOD) of 2.8 ng/mL was obtained. The method was successfully applied for the determination of FeCNs in a series of dietary food salt samples and gave satisfactory results; the spiked recoveries were 97.6‒104.6% with standard uncertainty less than 5.8%. The method proved to be applicable for ultra-trace detection of FeCNs in food salt samples, having advantages in great simplicity, rapid response, low cost, favourable selectivity, and high sensitivity.

Photothermal and colorimetric dual mode detection of nanomolar ferric ions in environmental sample based on in situ generation of prussian blue nanoparticles.

Iron ions play a key role in many physiological processes, which can provide feedback for the evaluation of biological systems and environmental processes. New strategies for portable determination of Fe3+ therefore are still in urgent need. Here, through an in situ generation of prussian blue nanoparticles (PB NPs) in aqueous solution, we developed a bimodal method for photothermal and colorimetric detection of Fe3+. The sensing mechanism is based on the effective oxidation etching of Au-Cu core-shell nanocubes induced by Fe3+, accompanied by the in situ generation of PB NPs. It can be attributed to the specific reaction between ferrous ions (Fe2+) from the reduction of Fe3+ and potassium ferricyanide (K3[Fe(CN)6]) in the reaction solution. The in situ produced PB NPs show distinct bare-eye-detectable readouts with highly sensitive colorimetric and photothermal responses and thus can be used for Fe3+ determination. Such colorimetric change signals of characteristic absorbance at 740 nm in the UV-vis spectra showed a sensitive response to Fe3+ with a LOD of 210 nM. Moreover, as a sensitive photothermal probe, PB NPs generated in our Fe3+-enabled reaction system also exhibited a sensitive response to Fe3+ with a LOD of 70 nM. In addition, the standard addition experiments demonstrate our photothermal and colorimetric probe has good applicability for Fe3+ detection in the river water sample. What's more, the proposed strategy opens a new horizon for affordable detection of metal ions using a common thermometer, and therefore has a great potential for analytical chemistry and some important applications such as environmental monitoring, disease diagnostics and food analysis.

Current Innovations of Metal Hexacyanoferrates-Based Nanocomposites toward Electrochemical Sensing: Materials Selection and Synthesis Methods.

Mixed valence transition metal hexacyanoferrates (MeHCF)-Prussian blue and its analogs receive enormous research interest in the electrochemical sensing field. In recent years, conducting materials such as conducting polymer, carbon nanomaterial, and noble metals have been used to form nanocomposites with MeHCF. The scope of this review offers the reasons behind the preparation of various MeHCF based nanocomposite toward electrochemical detection. We primarily focus on the current progress of the development of MEHCF-based nanocomposites. The synthesis methods for these nanocomposites are also reviewed and discussed.

Thermal remediation of cyanide-contaminated soils：process optimization and mechanistic study.

Site soils with persistent cyanide compounds (primarily iron-cyanide complex) pose potential hazards to the environment and require remediation before redevelopment. This study evaluated the possibility of thermal treatment on remediation of cyanide-contaminated soils via batch heating experiments spanning a wide temperature range (200-500 °C). The change with operation variables of total cyanide and some reaction intermediates (e.g. CN-) was analyzed in order to elucidate the optimal variables that guarantee cyanide removal while generating no hazardous byproducts. Temperature, heating time and cyanide species have been found to be important parameters influencing removal/destruction of cyanide in soils. For soils bearing K3[Fe(CN)6] and K4[Fe(CN)6], a removal efficiency of >99.9% can be obtained with temperatures over 350 °C at 1 h, while for samples bearing Fe4[Fe(CN)6]3, a higher temperature (>450 °C) is needed to obtain an equivalent efficiency. During heating, the iron-cyanide complexes decomposed, releasing highly toxic free cyanides, which will subsequently be oxidized. However, a small percentage of free cyanide can always be detected as a result of incomplete oxidation, thus caution should be taken to minimize the accumulation of free cyanide during thermal treatment.

A sensitivity enhanced fluorescence method for the detection of ferrocyanide ions in foodstuffs using carbon nanoparticles as sensing agents.

A novel fluorescent nanoprobe was for the first time developed for the efficient detection of ferrocyanide ions ([Fe(CN)6]4-) based on nitrogen (N), sulfur (S) and chlorine (Cl) co-doped carbon nanoparticles (N,S,Cl-CNPs). The N,S,Cl-CNPs were fabricated through a simple and ultrafast acid-base neutralization method. The sensing mechanism was based on the quenching effect of [Fe(CN)6]4- on the fluorescence emission of N,S,Cl-CNPs via dynamic interaction. The N,S,Cl-CNPs were found to show high selectivity and sensitivity towards [Fe(CN)6]4- detection with two good linear relationships were achieved in the concentration ranges of 0.01-1.0 µg/mL and 1.0-50.0 µg/mL, respectively, and the detection limits are as low as 3.3 and 21.8 ng/mL, respectively. The proposed fluorescence method was successfully applied for [Fe(CN)6]4- analyses in food samples with high accuracy. The results of this study indicate the great application prospects of N,S,Cl-CNPs for [Fe(CN)6]4- detection in complex food matrix.

Determination of potassium ferrocyanide in table salt and salted food using a water-soluble fluorescent silicon quantum dots.

The addition of potassium ferrocyanide (K4[Fe(CN)6]) in table salt as anti-caking agent has a crucial role in preventing the formation of lumps. However, the excess of K4[Fe(CN)6] and its decomposers are harmful to both human health and environment. To date, there are still lack of suitable methods for simple and rapid analysis of K4[Fe(CN)6] in table salt and salted food. Herein, a novel fluorescent Si QDs probe for sensitive, selective and rapid detection of K4[Fe(CN)6] was synthesized by facile one-step strategy. Notably, the fluorescence of Si QDs could be remarkably quenched by K4[Fe(CN)6] via electrostatic interaction. Based on this phenomenon, a new method of determination of K4[Fe(CN)6] was established. A wide linear range was obtained from 0.05 to 8.0 µg/mL with a detection limit of 30 ng/mL. The established fluorescent new method was suitable for detecting K4[Fe(CN)6] in table salt and salted food samples with satisfactory results.

Is the Cooking Salt Safe in China? Assessment of Chemical Contaminants in Cooking Salt.

Global environmental pollution is becoming more serious, and most dietary salts come from nature. We postulated that chemical pollutants could affect the quality of salt. Forty-five different types of salt were collected from supermarkets, convenience stores, and online retailers in Shanghai, 2015. These comprised more than 90% of all cooking salts consumed in Shanghai, China. We measured and analyzed heavy metal elements, fluoride, potassium ferrocyanide, and 16 phthalate plasticizers. Lead was detected in only two types of salt at concentrations recorded of 0.047 mg/kg and 0.077 mg/kg. The concentrations of total arsenic, total mercury, cadmium, and barium were under limit of detection (LOD) in all samples. The maximum fluoride concentration of salts was 2.50 mg/kg. The median fluoride concentration of domestic salts was significantly lower than foreign-produced salts, and it was significantly higher in sea salt than in other types of salt (P < 0.05). The maximum potassium ferrocyanide concentration in 12 types of salts was 9.20 mg/kg, which was under the Chinese national standard. Just three salt types had low levels of diethylhexyl phthalate concentrations that were above the LOD, at 0.208 mg/kg, 0.375 mg/kg, and 0.380 mg/kg, respectively. All other phthalate indicators were below the LOD in all samples. The level of chemical pollutants in salt is either very low or under LOD. We believe that dietary salt products are safe at retail, and the long-term dietary exposure of cooking salts will not pose any significant health risk.

Detoxification of ferrocyanide in asoil-plant system.

The detoxification of iron cyanide in a soil-plant system was investigated to assess the total cyanide extracted from contaminated soil and allocated in the leaf tissue of willow trees (Salix caprea). They were grown in soil containing up to 1000 mg/kg dry weight (dw) of cyanide (CN), added as 15N-labeled potassium ferrocyanide and prepared with a new method for synthesis of labeled iron cyanides. CN content and 15N enrichment were monitored weekly over the exposure in leaf tissue of different age. The 15N enrichment in the young and old leaf tissue reached up to 15.197‰ and 9063‰, respectively; it increased significantly over the exposure and with increasing exposure concentrations (p < 0.05). Although the CN accumulation in the old leaf tissue was higher, compared to the young leaf tissue (p < 0.05), the 15N enrichment in the two tissue types did not differ statistically. This indicates a non-uniform CN accumulation but a uniform 15N allocation throughout the leaf mass. Significant differences were detected between the measured CN content and the C15N content, calculated from the 15N enrichment (p < 0.05), revealing a significant CN fraction within the leaf tissue, which could not be detected as ionic CN. The application of labeled iron CN clearly shows that CN is detoxified during uptake by the willows. However, these results do not exclude other detoxification pathways, not related to the trees. Still, they are strongly indicative of the central role the trees played in CN removal and detoxification under the experimental conditions.

Direct Observation of Oxidation Reaction via Closed Bipolar Electrode-Anodic Electrochemiluminescence Protocol: Structural Property and Sensing Applications.

In this work, we developed an innovative closed bipolar electrode (BPE)-electrochemiluminescence (ECL) sensing strategy with generality for target detection. Based on charge balance and 100% current efficiency between the closed BPE poles and the driving electrodes, one of the driving electrodes in one cell of the closed BPE system was employed as ECL sensing surface to reflect the target on the BPE pole in the opposite cell. Compared with traditional BPE-ECL sensing method, which in general adopted the anodic ECL reagents such as Ru(bpy)32+ and its coreactant on one pole (anode) to reflect the target (occurring reduction reaction) on the other pole (cathode), the difference was that the targets occurring oxidation reaction could be detected by the anodic ECL reagents based on this strategy. To verify the feasibility of this strategy, the detection principle was stated first, and Fe(CN)64- as model target at anodic BPE pole were detected by anodic ECL reagents (Ru(bpy)32+ and TprA) on the driving electrode first. The ECL signals showed good performance for target detection. By changing the size and the material of the BPE pole where the targets were located, the detection of l-ascorbic acid (AA), uric acid (UA), and dopamine (DA) as other model targets with higher detection limit were accomplished. Visual and high-throughput detection of AA, UA, and DA were also successfully realized by an array of the closed BPE system. This closed BPE (array) system is an effective supplement of traditional BPE-ECL sensing and could greatly expand the scope of the detection target.

Development and validation of HPLC method for the determination of ferrocyanide ion in food grade salts.

A rapid, simple, and reliable HPLC method was developed and validated to determine the presence of ferrocyanide ions (FeCNs) in food grade salts. An analytical column coupled with a guard column and mobile phase comprised of sodium perchlorate and sodium hydroxide (NaOH) were employed at a detection wavelength of 221nm. Samples were dissolved in 0.02M NaOH solution and filtered. For processed salts including herbs and spices, a C18 cartridge was applied to minimize interference from salt matrices. The method validation was based on linearity, accuracy (recovery), precision, LOD, LOQ, and measurement uncertainty. This method exhibits good linearity from 0.1-10mg/L (r2=0.9999). The LOD and LOQ values were determined to be 0.02 and 0.07mg/kg, respectively. The FeCN recoveries in six salt matrices ranged from 80.3-102.2% (RSD=0.3-4.4%). These results indicate that the proposed method is suitable for FeCN ion determination in various food grade salts.

Photoacoustic Imaging of Human Mesenchymal Stem Cells Labeled with Prussian Blue-Poly(l-lysine) Nanocomplexes.

Acoustic imaging is affordable and accessible without ionizing radiation. Photoacoustic imaging increases the contrast of traditional ultrasound and can offer good spatial resolution when used at high frequencies with excellent temporal resolution. Prussian blue nanoparticles (PBNPs) are an emerging photoacoustic contrast agent with strong optical absorption in the near-infrared region. In this study, we developed a simple and efficient method to label human mesenchymal stem cells (hMSCs) with PBNPs and imaged them with photoacoustic imaging. First, PBNPs were synthesized by the reaction of FeCl3 with K4[Fe(CN)6] in the presence of citric acid and complexed with the cationic transfection agent poly-l-lysine (PLL). The PLL-coated PBNPs (PB-PLL nanocomplexes) have a maximum absorption peak at 715 nm and could efficiently label hMSCs. Cellular uptake of these nanocomplexes was studied using bright field, fluorescence, and transmission electron microscopy. The labeled stem cells were successfully differentiated into two downstream lineages of adipocytes and osteocytes, and they showed positive expression for surface markers of CD73, CD90, and CD105. No changes in viability or proliferation of the labeled cells were observed, and the secretome cytokine analysis indicated that the expression levels of 12 different proteins were not dysregulated by PBNP labeling. The optical properties of PBNPs were preserved postlabeling, suitable for the sensitive and quantitative detection of implanted cells. Labeled hMSCs exhibited strong photoacoustic contrast in vitro and in vivo when imaged at 730 nm, and the detection limit was 200 cells/µL in vivo. The photoacoustic signal increased as a function of cell concentration, indicating that the number of labeled cells can be quantified during and after cell transplantations. In hybrid ultrasound/photoacoustic imaging, this approach offers real-time and image-guided cellular injection even through an intact skull for brain intraparenchymal injections. Our labeling and imaging technique allowed the detection and monitoring of 5 × 104 mesenchymal stem cells in living mice over a period of 14 days.

Portable Lock-in Amplifier-Based Electrochemical Method to Measure an Array of 64 Sensors for Point-of-Care Applications.

We present a portable lock-in amplifier-based electrochemical sensing system. The basic unit (cluster) consists of four electrochemical cells (EC), each containing one pseudoreference electrode (PRE) and one working electrode (WE). All four ECs are simultaneously interrogated, each at different frequencies, with square wave pulses superposed on a sawtooth signal for cyclic voltammetry (CV). Lock-in amplification provides independent read-out of four signals, with excellent noise suppression. We expanded a single cluster system into an array of 16 clusters by using electronic switches. The chip with an array of ECs was fabricated using planar technology with a gap between a WE and a PRE of ≈2 µm, which results in partial microelectrode-type behavior. The basic electrode characterization was performed with the model case using a ferricyanide-ferrocyanide redox couple (Fe2+/Fe3+) reaction, performing CV and differential pulse voltammetry (DPV). We then used this system to perform cyclic lock-in voltammetry (CLV) to measure concurrently responses of the four ECs. We repeated this method with all 64 ECs on the chip. The standard deviation of a peak oxidation and reduction current in a single channel consisting of 13 ECs was ≈7.46% and ≈5.6%, respectively. The four-EC configuration in each measured spot allows determination of nonperforming ECs and, thus, to eliminate potential false results. This system is built in a portable palm-size format suitable for point-of-care applications. It can perform either individual or multiple measurements of active compounds, such as biomarkers.

New method for characterizing electron mediators in microbial systems using a thin-layer twin-working electrode cell.

Microbial biofilms are significant ecosystems where the existence of redox gradients drive electron transfer often via soluble electron mediators. This study describes the use of two interfacing working electrodes (WEs) to simulate redox gradients within close proximity (250µm) for the detection and quantification of electron mediators. By using a common counter and reference electrode, the potentials of the two WEs were independently controlled to maintain a suitable "voltage window", which enabled simultaneous oxidation and reduction of electron mediators as evidenced by the concurrent anodic and cathodic currents, respectively. To validate the method, the electrochemical properties of different mediators (hexacyanoferrate, HCF, riboflavin, RF) were characterized by stepwise shifting the "voltage window" (ranging between 25 and 200mV) within a range of potentials after steady equilibrium current of both WEs was established. The resulting differences in electrical currents between the two WEs were recorded across a defined potential spectrum (between -1V and +0.5V vs. Ag/AgCl). Results indicated that the technique enabled identification (by the distinct peak locations at the potential scale) and quantification (by the peak of current) of the mediators for individual species as well as in an aqueous mixture. It enabled a precise determination of mid-potentials of the externally added mediators (HCF, RF) and mediators produced by pyocyanin-producing Pseudomonas aeruginosa (WACC 91) culture. The twin working electrode described is particularly suitable for studying mediator-dependent microbial electron transfer processes or simulating redox gradients as they exist in microbial biofilms.

Prussian blue type nanoparticles for biomedical applications.

Prussian blue type nanoparticles are exciting nano-objects that combine the advantages of molecule-based materials and nanochemistry. Here we provide a short overview focalizing on the recent advances of these nano-objects designed for biomedical applications and give an outlook on the future research orientations in this domain.

Synthesis of acid-stabilized iron oxide nanoparticles and comparison for targeting atherosclerotic plaques: evaluation by MRI, quantitative MPS, and TEM alternative to ambiguous Prussian blue iron staining.

To further optimize citrate-stabilized VSOPs (very small iron oxide particles, developed for MR angiography) for identification of atherosclerotic plaques, we modified their surface during synthesis using eight other acids for electrostatic stabilization. This approach preserves effective production for clinical application. Five particles were suitable to be investigated in targeting plaques of apoE(-/-) mice. Accumulation was evaluated by ex vivo MRI, TEM, and quantitatively by magnetic particle spectroscopy (MPS). Citric- (VSOP), etidronic-, tartaric-, and malic-acid-coated particles accumulated in atherosclerotic plaques with highest accumulation for VSOP (0.2‰ of injected dose). Targets were phagolysosomes of macrophages and of altered endothelial cells. In vivo MRI with VSOP allowed for definite plaque identification. Prussian blue staining revealed abundant endogenous iron in plaques, indistinguishable from particle iron. In apoE(-/-) mice, VSOPs are still the best anionic iron oxide particles for imaging atherosclerotic plaques. MPS allows for quantification of superparamagnetic nanoparticles in such small specimens. FROM THE CLINICAL EDITOR: The presence of vulnerable plaques in arteries is important for the prediction of acute coronary events. VSOP (very small iron oxide particles, developed for MR angiography) have been shown to be very sensitive in identifying atherosclerotic plaques. The authors studied here further modification to the surface of VSOP during synthesis and compared their efficacy.

Retardation of iron-cyanide complexes in the soil of a former manufactured gas plant site.

The soil in the vicinities of former Manufactured Gas Plant (MGP) sites is commonly contaminated with iron-cyanide complexes (ferric ferrocyanide). The phenomenon of cyanide mobility in soil, according to the literature, is mainly governed by the dissolution and precipitation of ferric ferrocyanide, which is only slightly soluble (<1 mg L(-1)) under acidic conditions. In this paper, retention properties of the sandy loam soil and the potential vertical movement of the solid iron-cyanide complexes, co-existing with the dissolution, sorption and precipitation reactions were investigated. Preliminary research conducted on a former MGP site implied colloidal transport of ferric ferricyanide from the initial deposition in the wastes layer towards the sandy loam material (secondary accumulation), which possibly retarded the mobility of cyanide (CN). A series of batch and column experiments were applied in order to investigate the retardation of iron-cyanide complexes by the sandy loam soil. Batch experiments revealed that in circumneutral pH conditions sandy loam material decreases the potassium ferro- and ferricyanide concentration. In column experiments a minor reduction in CN concentration was observed prior to addition of iron sulfide (FeS) layer, which induced the formation of the Prussian blue colloids in circumneutral pH conditions. Precipitated solid iron-cyanide complexes were mechanically filtered by the coherent structure of the investigated soil. Additionally, the reduction of the CN concentration of the percolation solutions by the sandy loam soil was presumably induced due to the formation of potassium manganese iron-cyanide (K2Mn[Fe(CN)6]).

Simultaneous multiselective spectroelectrochemical fiber-optic sensor: demonstration of the concept using methylene blue and ferrocyanide.

Herein, we present a novel spectroelectrochemical fiber-optic sensor that combines electrochemistry, spectroscopy, and electrostatic adsorption in three modes of selectivity. The proposed sensor is simple and consists of a gold mesh cover on a multimode fiber optic that uses attenuated total reflection as the optical detection mode. The sensing is based on changes in the attenuation of the light that passes through the fiber-optic core accompanying the electrochemical oxidation-reduction of an analyte at the electrode. Methylene blue and ferrocyanide were used as model analytes to evaluate the performance of the proposed sensor. The optical transmission changes generated by electrochemical manipulation showed a good linear relationship with the concentration and the limits of detection (3σ) for methylene blue and ferrocyanide at 2.0 × 10(-7) and 1.6 × 10(-3) M, respectively. The sensor responses were successfully enhanced with an additional level of selectivity via an electrostatically adsorbed, self-assembled monolayer (SAM), which consisted of a silane coupling layer, a polyanion, and a polycation. The improvement observed in the sensitivity of a SAM-modified fiber-optic sensor was rather encouraging. The optimized sensor had detection limits (3σ) of 8.3 × 10(-9) M for methylene blue and 7.1 × 10(-4) M for ferrocyanide. The developed sensor was successfully applied to the detection of ferrocyanide in simulated nuclear waste.

Stability improvement of Prussian blue in nonacidic solutions via an electrochemical post-treatment method and the shape evolution of Prussian blue from nanospheres to nanocubes.

In this study we report the improved stability of Prussian blue (PB) films in neutral and alkaline solutions via an electrochemical post-treatment procedure. In this procedure, PB films synthesized via the electroless deposition method at glassy carbon electrodes were continuously cycled for 300 cycles (∼12 h) between the potential limits of +0.6 and -0.1 V (vs. Ag/AgCl) at a scan rate of 10 mV s(-1) in 2.0 M KCl solution of pH 3. It was found that after such electrochemical post-treatment the PB films exhibit dramatically improved stability in neutral and alkaline solutions. Control experiments confirmed that the longer potential cycling time and the higher KCl concentration are indispensable. In addition, interestingly, it was found that after the successive potential cycling treatments the shape of PB nanoparticles evolves from a sphere into a cube as well as a small amount of a rectangle, indicating the electrochemically induced shape evolution of nanocrystals. The electrochemical post-treatment procedure proposed here could be useful for the development of PB-based devices with improved stability, for instance, biosensors, biofuel cells, etc.