Plasmonic and nanozyme dual-channel-based logic judgment for enhancing gold nanoparticle based colorimetric Hg2+ ion sensing performance.

An AND logic gate-based Hg2+ ion colorimetric assay was constructed using the plasmonic and nanozyme dual signal channels of gold nanoparticles (AuNPs). This assay increased the judgment criteria for the identification of Hg2+ ions and effectively improved the accuracy of Hg2+ ion detection.

Propanediamine modified pillar[5]arene: A novel stationary phase for the high selectivity separation of versatile analytes.

The unique properties of pillar[5]arene, including hydrophobic cavities, π-π conjugated and easy modification, make it a promising candidate as stationary phase for HPLC. Herein, we fabricated a novel propanediamine modified pillar[5]arene bonded silica as the stationary phase (PDA-BP5S) for reversed-phase liquid chromatography (RPLC). Benefiting from the significant hydrophobicity, π-π conjugative, p-π effect, and hydrogen bonding, the PDA-BP5S packed column showed high separation performance of versatile analytes involving polycyclic aromatic hydrocarbons, alkyl benzenes, phenols, arylamine, phenylethane/styrene/ phenylacetylene, toluene/m-xylene/mesitylene, halobenzenes, benzenediol and nitrophenol isomers. Especially, the separation of halobenzenes appeared to be controlled by both the size of the halogen substituents and the strength of the noncovalent bonding interactions, which was further confirmed by molecular dynamics simulation. The satisfactory separation and repeatability revealed the promising prospects of amine-pillar[5]arene-based stationary phase for RPLC.

Ultra-rapid and highly selective colorimetric detection of hydrochloric acid via an aggregation to dispersion change of gold nanoparticles.

A rapid and highly selective naked-eye detection of hydrochloric acid (HCl) in an aqueous medium was established using HCl-triggered redispersion of gold nanoparticle aggregates.

A novel top-down strategy for in situ construction of vertically oriented hexagonal NiCr LDHs nanosheet arrays with intercalated sulfate ions on Nichrome fiber for selective solid-phase microextraction of phenolic compounds in water samples.

BACKGROUND: Phenolic compounds (PCs) are a class of polar aromatic pollutants with high toxicity in environmental water. Generally the efficient sample preparation is essential for the quantification of ultra-trace target PCs in real water sample before appropriative instrumental analysis. SPME is a convenient, solvent-free and time-saving miniaturized technique and has been recognized as a green alternative to conventional extraction techniques. In SPME, however, commercial fused-silica fibers are limited to the fragility, operation temperature, extraction capacity and selectivity as well as lifetime. Therefore, the development of new SPME fibers is always needed to overcome such limitations. RESULTS: We presented a novel top-down strategy for in situ construction of vertically oriented hexagonal sulfate intercalated NiCr layered double hydroxide nanosheet arrays (NiCr LDHs-SO4 NSAs) on the Nichrome (NiCr) substrate by hydrothermal treatment in NaOH solution containing (NH4)2S2O8. The results showed that much shorter hydrothermal time was needed for the construction of NiCr@NiCr LDHs-SO4 NSAs fiber in the presence of (NH4)2S2O8. Moreover, the unique NiCr LDHs-SO4 NSAs coating offered open access structure, and thereby more available surface area for adsorption. The resulting fiber exhibited better extraction efficiency for phenolic compounds (PCs), faster mass transfer rate, higher mechanical stability, and longer service life than original NiCr@NiCr LDHs NSs fiber and typical commercially fused-silica fibers. After optimizing conditions, the SPME-HPLC-UV method demonstrated a linear range from 0.05 µg L-1 to 200 µg L-1 with LODs of 0.015-0.156 µg L-1 (S/N = 3) and LOQs of 0.048-0.498 µg L-1 (S/N = 10), as well as good repeatability (3.06%-5.22%) and fiber-to-fiber reproducibility (4.32%-6.49%). SIGNIFICANCE: The developed SPME-HPLC-UV method with the constructed fiber was applied to the preconcentration and detection of different types of PCs in real water samples, showing satisfactory recoveries ranging from 86.20% to 107.8% with RSDs of 3.18%-6.69%. This study provides a new strategy for in situ construction of bimetallic hydroxides and their derived nanocomposite coatings on the NiCr fiber substrate in practical SPME application.

A label-free and modification-free ratiometric electrochemical strategy for enhanced natural enzyme detection using a bare electrode and nanozymes system.

Ratiometric electrochemical assays have been demonstrated to be more sensitive and selective in various sensing events, mainly due to their affordable built-in correction and good self-reference capability. But it is known that complicated modification and labeling operations usually are necessary for the construction of ratiometric electrochemical assays, therefore is a hot and important issue needing consideration carefully. We herein report a new yet simple bare electrode-based ratiometric electrochemical bioassay to achieve sensitive and selective analysis of alkaline phosphatase (ALP), using a liquid phase system that contains CoOOH nanozymes and commercially available indicator substrate. This proposed bioassay works based on the ratiometric change of dual electrochemical signals, arising from an exclusive target ALP-triggered hydrolysis of electrochemical substrate p-nitrophenyl phosphate (PNPP). In this design, the two hydrolyzed products of electrochemically active p-nitrophenol (PNP) and electrochemically inactive phosphate anion (PO43-) are responsible together for the ratiometric electrochemical analysis of ALP. PNP exhibits a straightforward current response toward ALP content; however, PO43- cannot show a direct electrochemical signal thus is rationally designed to offer an alternative response by linking it with the specific CoOOH nanozyme-catalyzed reaction of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2, in which the nanozyme-catalyzed product oxTMB shows a direct reduction current at the GCE, and significantly decreases with increasing PO43- species due to the good inhibition of PO43- toward CoOOH nanozyme activity. As a result, a ratiometric electrochemical strategy for ALP analysis with a low limit of detection of 0.366 U/L (S/N = 3) was successfully achieved by integrating the above direct and indirect dual electrochemical responses. This developed bioassay can allow the quantitative diagnosis of ALP activity especially with a label-free and modification-free merit, therefore paving the way for simple, convenient, and portable electroanalytical tools in biosensing design and application.

Nanoporous germanium prepared by a mechanochemical reaction with enhanced lithium storage properties.

The cost-effective and facile fabrication of nanostructured germanium for lithium-ion batteries (LIBs) remains a grand challenge. Herein, nanoporous Z-Ge was generated via a facile two-step mechanochemical-etching reaction with Mg2Ge and ZnCl2. The prepared nanoporous Ge nanoparticles, as the anode for Li-Ge half cells, showed superior LIB performance, in terms of a high capacity, good rate capability, and good long-term stability of 700 cycles. Significantly, the mechanochemical reaction was extended to produce other nanoporous Ge or Si materials such as A-Ge, Z-Si, and A-Si via the mechanochemical reaction between Mg2Ge and AlCl3, Mg2Si and ZnCl2, and Mg2Si and AlCl3.

A sensitive photothermometric biosensor based on redox reaction-controlled nanoprobe conversion from Prussian blue to Prussian white.

As a new low-cost photothermal nanoprobe, Prussian blue nanoparticles (PB NPs) have been demonstrated to have more potential in photothermometric-based point-of-care testing (POCT) application. However, most of the existing PB NP-based photothermometric sensors were constructed mainly relying on in situ generation of PB NPs or their combination with antigens and antibodies, therefore usually suffering from the inherent defects like complicated preparation and cumbersome surface process as well as high-cost modification. To break this limitation of PB NP-based photothermometric POCT, we proposed an ingenious redox reaction-controlled nanoprobe conversion strategy and successfully applied to photothermometric detection of ascorbate oxidase (AAO). In this design, the heat of PB NP photothermal system under 808-nm laser irradiation dramatically decreased with the addition of AA, due to a unique AA-induced Prussian blue to Prussian white (PB-to-PW) conversion. Upon AAO addition, the heat of reaction system increased because of the enzymatic catalytic reaction between AAO and AA, which led to a significant reduction of AA and resultantly inhibited PB-to-PW conversion. Such target-mediated nanoprobe conversion resulted in an obvious temperature change that could be easily detected by a common thermometer and exhibited good linear ranges from 0.25 to 14 mU/mL with a detection limit as low as 0.21 mU/mL for POCT analysis of AAO. This facile, convenient, and portable photothermometric sensing platform provides an innovative route for the design of PB NP nanoprobe-based photothermometric detection methods. A sensitive photothermometric AAO sensor based on a redox reaction-controlled nanoprobe conversion strategy from Prussian blue to Prussian white.

Integration of organic and inorganic photothermal probes for enhanced photothermometric sensing of silver ions.

A new signal-amplified photothermometric sensor of Ag+ was explored based on a simple yet effective integration of inorganic and organic photothermal probes, mainly depending on the successful exploitation of a dual-signal transduction channel originating from the inherent photothermal property and the peroxidase-like activity of Prussian blue nanocubes (PB NCs).

A two fluorescent signal indicator-based ratio fluorometric alkaline phosphatase assay based on one signal precursor.

Two fluorescent signal indicators were simply converted from one organic precursor system by using the superior oxidation capability of manganese dioxide (MnO2) nanosheets for the first time, finally resulting in the successful fabrication of a ratio fluorometric bioassay of alkaline phosphatase (ALP).

A Fenton-like reaction system with analyte-activated catfish effect as an enhanced colorimetric and photothermal dopamine bioassay.

Fenton-like reaction systems have been proven to be efficient as powerful promoters in advanced oxidation processes (AOPs) due to their generated reactive oxygen species (ROS), such as ˙OH and ˙O2-, which can further oxidize a specific chromogenic substrate like 3,3',5,5'-tetramethylbenzidine (TMB) to generate sensitive color readout and thereby demonstrate more potential in the colorimetric analysis field. However, the inherent drawback of the low rate-limiting step of Fe3+/Fe2+ conversion in the Fenton-like reaction and its resultant inefficiency for H2O2 decomposition hinder its practical applications. We herein communicate an analyte-activated catfish effect based catalysis strategy to promote the Fenton-like reaction, in which dopamine, like a catfish, was added to activate the Fenton-like reaction. By definition, the conversion rate of Fe3+ to Fe2+ in the proposed Fenton-like reaction can be significantly accelerated through a specific DA-mediated electron transfer process which further promotes the reaction activity in the Fenton-like reaction to generate more ˙OH and ˙O2- radicals. As a result, the produced ˙OH and ˙O2- radicals in such a reaction system can significantly oxidize TMB indicator into its oxidation product (TMBox) and therefore indicate the corresponding target-dependent color and photothermal signal readout, enabling the successful fabrication of a more sensitive and stable colorimetric and photothermometric DA sensor. More significantly, this strategy can greatly advance the practical application of Fenton-like reactions in the fields of colorimetric and photothermometric bioassays.

Gold nanozyme as an excellent co-catalyst for enhancing the performance of a colorimetric and photothermal bioassay.

Advanced oxidation processes (AOPs) have recently proposed for advancing colorimetric sensing applications, owing to their excellent performance of sensitive color readout that generated from the oxidation of chromogenic substrates like 3,3',5,5'-tetramethylbenzidine (TMB) by reactive oxygen species (ROS) of AOPs such as ·OH and ·O2- radicals. However, the efficiency of ROS generation and the related H2O2 decomposition in most AOPs is quite low especially at neutral pH, which greatly hampered the practical sensing applications of the AOPs. We herein communicated that ß-cyclodextrin (ß-CD)-capped gold nanoparticles (ß-CD@AuNPs) can promote catalysis at neutral pH for AOP as an excellent co-catalyst. In this strategy, inorganic pyrophosphate (PPi) ions was first used to coordinate with Cu2+ and form Cu2+-PPi complex. In the presence of hydrogen peroxide, target inorganic pyrophosphatase (PPase) can hydrolyze PPi into inorganic phosphate (Pi) and release free Cu2+ simultaneously, resulting in a Cu2+-triggered Fenton-like AOP reaction. The introduced ß-CD@AuNPs acts as a co-catalyst, analogous to mediators in the most co-catalyzed system, to enhance the rate-limiting step of Cu2+/Cu+ conversion in Cu2+/H2O2 Fenton-like AOP and resulting in an efficient generation of ·OH and ·O2- radicals, which further producing an intense blue color by oxidizing TMB into its oxidation product (TMBox) within a short time. Finally, this reaction system was used to simply detecting target PPase with the colorimetric and photothermal readout based on the in-situ generated TMBox indicator. More significantly, we successfully demonstrated nanozyme can serve as a co-catalyst to promote the AOP catalysis at neutral pH, and inspire other strategies to overcome the pH limitation in the AOP catalysis and expand its colorimetric and photothermometric application.

Simply translating mercury detection into a temperature measurement: using an aggregation-activated oxidase-like activity of gold nanoparticles.

A novel Hg2+-responsive thermometer system for translating mercury detection into temperature monitoring was developed based on an aggregation-activated oxidase-like activity of gold nanoparticles.

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.

Enhanced Thermometric Sensor for Arsenate Analysis Based on Dual Temperature Readout Signaling Strategy.

New methods for portable detection of arsenate are still in urgent need. Herein, we explored a simple but sensitive thermometric strategy for arsenate determination without complex instruments and skilled technicians. Cobalt oxyhydroxide (CoOOH) nanoflakes, can ingeniously decompose hydrogen peroxide into oxygen in a sealed reaction vessel, accompanied by marked pressure and significant temperature increase due to the exothermic reaction effect (ΔH = -98.2 kJ/mol). The increased pressure then compelled a certain amount of H2O overflowing from the drainage device into another vessel, leading to a significant temperature decrease due to the preloaded ammonium nitrate (NH4NO3) and its good dissolution endothermic effect (ΔH = 25.4 kJ/mol). In the presence of arsenate, the catalytic activity of CoOOH nanoflakes for H2O2 decomposition was inhibited dramatically, resulting in an obvious decrease of the pressure, weighting water and temperature response. The two temperature responses with increasing and decreasing feature were easily measured through a common thermometer, and exhibited an effective signaling amplification via coupling both "signal-on" and "signal-off" temperature readout elements. The obtained dual superimposing temperature readout exhibits a good linear with the concentration of arsenate with a lower detection limit (51 nM, 3.8 ppb). Compared to the inductively coupled plasma mass spectrometry, this enhanced thermometric strategy provides a simple, rapid, convenient, low cost, and portable platform for sensing arsenate in real environmental water.

Target-mediated surface chemistry of gold nanorods for breaking the low color resolution limitation of monocolorimetric sensor.

A long-term limitation of low color resolution in the monocolorimetric sensors seriously restricts its extending application, especially for the traditional organic dyes-based monocolorimetric sensors. Herein, we explore a simple target-mediated surface chemistry-based modulation for regulating the surface of gold nanorods (AuNRs), resulting in a successful multicolorimetric sensor for inorganic pyrophosphatase (PPase) activity. It operates on the principle that PPase modulates the release of Fe3+ free from the ferric-pyrophosphate complex (Fe3+-PPi) through a specific target-catalyzed hydrolysis process, leading to a better mediation for the unique chemical redox reaction between Fe3+ and I-. Subsequently, I- is oxidized into I2, which as a moderate oxidant further regulates the surface of AuNRs due to the rapidly etching reaction between I2 and AuNRs. As a result, the resultant AuNRs surface change further leads to a blue-shift longitudinal LSPR effect of AuNRs, along with a naked-eye-detectable rainbow-like multicolor signal readout. Under optimal conditions, the proposed multicolorimetric sensor exhibits an affordable sensing performance for PPase activity in the range from 1.5 U L-1 to 9 U L-1 with a detection limit of 0.8 U L-1 (S/N = 3). To this point, our strategy not only provides a promising way for breaking the low color resolution limitation of the traditional monocolorimetric sensors, but also broadens the applicability of AuNRs etching-based multicolorimetric sensors.

Molecule-gated surface chemistry of Pt nanoparticles for constructing activity-controllable nanozymes and a three-in-one sensor.

Herein, a simple strategy for constructing activity-controllable nanozymes is proposed based on the glutathione (GSH)-gated surface chemistry of citrate-capped Pt nanoparticles (PtNPs). PtNPs have been shown to have oxidase-like activity that can effectively catalyze the oxidation of 3,3',5,5'-tertamethylbenzidine (TMB) by O2, resulting in a typical color reaction from colorless to blue. We found that GSH can inhibit the oxidase-like activity of PtNPs as a molecule-gated surface chemistry element, resulting in a dramatic decrease of the oxidation of TMB. The addition of copper ions (Cu2+) could oxidize GSH into glutathione disulfide (GSSG), resulting in the distinct suppression of GSH-modulated PtNP surface chemistry and oxidase-like activity inhibition, which further results in a significant acceleration of TMB oxidation and the obvious recovery of intense blue color. Furthermore, the color-based detection signal associated with the redox of TMB indicator here was found to show good fluorescence and a photothermal effect and exhibit sensitive and selective response toward the proposed molecule-gated surface chemistry and Cu2+ target. On the basis of this phenomenon, we successfully constructed a three-in-one sensor for Cu2+ with a triple signal readout, colorimetric, photothermal (temperature), and fluorescence, depending on the proposed in situ modulation method for PtNP catalysis. The applicability of the three-in-one sensor was also demonstrated by measuring Cu2+ in human serum with a standard addition method, and the results are of satisfactory accuracy as confirmed by ICP-MS measurements.

A colorimetric sensor of cysteine based on self-assembly nanostructures of Fe3+-H2O2/Tetramethylbenzidine system with "On-Off" switching function.

Many strategies have been explored for selectively and sensitively detecting cysteine in different samples. Here, a novel colorimetric sensor based on self-assembly nanostructures of Fe3+-H2O2/Tetramethylbenzidine system with dual-level logic gate function and colorimetric determination of cysteine were firstly explored. The proposed Fe3+-H2O2-TMB system provides a sensitive optical signal due to the selectively reductive ability of cysteine to the oxidized TMB and thus could be successfully applied to the construction of instant on-site visual detection method with a paper based test strip for cysteine determination in a sample solution as well as for a dual-level logic gate fabrication.

A colorimetric indicator-displacement assay for cysteine sensing based on a molecule-exchange mechanism.

In this study, we developed an ingenious yet effective strategy for cysteine detection. The colorimetric cysteine assay is established through an indicator displacement process, where Cu2+ and pyrocatechol violet (PV) was employed as receptor and indicator, respectively. Proof-of-concept trials demonstrated that the stronger binding affinity of Cu2+ receptor toward cysteine than PV indicator endowed our colorimetric sensor with high selectivity and excellent sensitivity as well as with a lower detection limit (4.60µM and 120µM, S/N =3) by UV-visible spectroscopy and the naked eye as the signal readout, respectively. More importantly, the proposed molecule-exchange process in the indicator displacement process could be successfully used to the fabrication of a colorimetric INHIBIT logic gate and even converted into a facile naked eye analysis through paper-based analytical devices for conveniently and reliably detecting cysteine (CySH) in practical applications.

Amperometric indicator displacement assay for biomarker monitoring: Indirectly sensing strategy for electrochemically inactive sarcosine.

Indicator displacement assay plays a fundamental role in the development of chemosensors. We explored here an ingenious yet effective strategy for amperometric assay of electrochemically inactive sarcosine based on an indicator displacement principle, in which 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS) was proposed as the receptor and the electroactive Ru(NH3)63+ cations used as an indicator. Due to the stronger binding affinity of the NQS toward sarcosine than toward Ru(NH3)63+, the developed amperometric indicator displacement assay (A-IDA) exhibits high selectivity and excellent sensitivity toward sarcosine determination as well as with a lower detection limit (30.00nM, S/N =3).

An organic indicator functionalized graphene oxide nanocomposite-based colorimetric assay for the detection of sarcosine.

Rapid detection of sarcosine is a key requirement for both diagnosis and treatment of disease. We report here a simple yet sensitive colorimetric nanocomposite platform for rapid detection of sarcosine in alkaline media. The approach exploited the benefits of a rapid color-producing reaction between an organic indicator, 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS), and the analyte of sarcosine species as well as the good catalytic ability of graphene oxide (GO) to the formation of highly colored products due to its good water dispersibility, extremely large surface area and facile surface modification. As a result, a NQS functionalized GO nanocomposite through π-π stacking has been demonstrated to be useful as a highly efficient catalyst system for the selective and sensitive colorimetric determination of sarcosine by providing a nanocomposite-amplified colorimetric response. Meanwhile, the strategy offered excellent selectivity toward sarcosine species against other amino acids as well as a satisfying detection limit of 0.73 µM. More importantly, by using an electrochemical method, a credible sensing mechanism of GO nanocomposite-based colorimetric platform for a special analyte determination can be easily verified and elucidated, which also provides an attractive alternative to conventional characterization strategies.