Quantitative analysis of a posterior fossa teratomas with unusual CT and MR Characteristics--illustrative case.

Background: Intracranial teratomas or other cystic lesions with atypical imaging manifestations can still be frequently seen clinically. The specific reasons for unusual imaging manifestations need to be further explored. Observations: A case of adult teratoma in the posterior fossa with unusual imaging manifestations was reported. The chemical composition of its cystic fluid was quantitatively detected, and in vitro imaging simulation experiments were performed on some fluid substances with similar cystic fluid properties to explore the reasons for special imaging manifestations. The content of inorganic substances and protein in the cystic fluid were both low, with no melanin detected. In vitro experiments revealed that MR T1 signals could increase with protein content rising and changes in MR T2 signals presented no obvious correlation with it. CT values increased gradually with protein concentration rising. The substances with similar viscosity had similar CT values, whereas substance viscosity showed no significant correlation with changes in MR signals. Conclusion: The abnormality of imaging manifestations cannot be confirmed as the result of "high protein content", nor can it be simply attributed to bleeding. Further research is required for the impact of the combination of paramagnetic particles and biofluid on imaging.

In Situ Enzymatically Generated Photoswitchable Oxidase Mimetics and Their Application for Colorimetric Detection of Glucose Oxidase.

In this study, a simple and amplified colorimetric assay is developed for the detection of the enzymatic activity of glucose oxidase (GOx) based on in situ formation of a photoswitchable oxidase mimetic of PO4(3-)-capped CdS quantum dots (QDs). GOx catalyzes the oxidation of 1-thio-ß-d-glucose to give 1-thio-ß-d-gluconic acid which spontaneously hydrolyzes to ß-d-gluconic acid and H2S; the generated H2S instantly reacts with Cd(2+) in the presence of Na3PO4 to give PO4(3-)-stabilized CdS QDs in situ. Under visible-light (λ ≥ 400 nm) stimulation, the PO4(3-)-capped CdS QDs are a new style of oxidase mimic derived by producing some active species, such as h⁺, (•)OH, O2(•-) and a little H2O2, which can oxidize the typical substrate (3,3,5,5-tetramethylbenzydine (TMB)) with a color change. Based on the GOx-triggered growth of the oxidase mimetics of PO4(3-)-capped CdS QDs in situ, we developed a simple and amplified colorimetric assay to probe the enzymatic activity of GOx. The proposed method allowed the detection of the enzymatic activity of GOx over the range from 25 µg/L to 50 mg/L with a low detection limit of 6.6 µg/L. We believe the PO4(3-)-capped CdS QDs generated in situ with photo-stimulated enzyme-mimicking activity may find wide potential applications in biosensors.

Label-free and ratiometric detection of nuclei acids based on graphene quantum dots utilizing cascade amplification by nicking endonuclease and catalytic G-quadruplex DNAzyme.

Herein, we report a ratiometric fluorescence assay based on graphene quantum dots (GQDs) for the ultrasensitive DNA detection by coupling the nicking endonuclease assisted target recycling and the G-quadruplex/hemin DNAzyme biocatalysis for cascade signal amplifications. With o-phenylenediamine acted as the substrate of G-quadruplex/hemin DNAzyme, whose oxidization product (that is, 2,3-diaminophenazine, DAP) quenched the fluorescence intensity of GQDs (at 460nm) obviously, accompanied with the emergence of a new emission of DAP (at 564nm). The ratiometric signal variations at the emission wavelengths of 564 and 460nm (I564/I460) were utilized for label-free, sensitive, and selective detection of target DNA. Utilizing the nicking endonuclease assisted target recycling and the G-quadruplex/hemin DNAzyme biocatalysis for amplified cascade generation of DAP, the proposed bioassay exhibited high sensitivity toward target DNA with a detection limit of 30fM. The method also had additional advantages such as facile preparation and easy operation.

Switchable fluorescence of gold nanoclusters for probing the activity of alkaline phosphatase and its application in immunoassay.

In this work, a novel strategy for modulating the fluorescence of gold nanoclusters (Au NCs) is developed. The fluorescence of bovine serum albumin (BSA) protected Au NCs is firstly quenched by KMnO4 and then restored by ascorbic acid (AA) due to the deterioration/restoration of the surface structure. Based on which, a novel "switch-on" fluorescent assay for probing the activity of alkaline phosphatase (ALP) is developed with a detection limit as low as 0.002 U/L. In addition, this testing protocol is also expanded to the detection of the inhibitor of ALP and mouse IgG (as a model), the detection limits are 15 ng/mL for the inhibitor of 2,4-Dichlorophenoxyacetic acid (2,4-DA) and 1.5 pg/mL for mouse IgG. The present method paves a new way to develop convenient, sensitive, and selective metal NCs-based fluorescent "turn-on" probes with promising applications in versatile biosensing.

Label-free colorimetric sensor for mercury(II) and DNA on the basis of mercury(II) switched-on the oxidase-mimicking activity of silver nanoclusters.

In this paper, a novel colorimetric biosensor for Hg(2+) and DNA molecules is presented based on Hg(2+) stimulated oxidase-like activity of bovine serum albumin protected silver clusters (BSA-Ag NCs). Under mild conditions, Hg(2+) activated BSA-Ag NCs to show high catalytic activity toward the oxidation of 3,3',5, 5'-tetramethylbenzidine (TMB) using ambient dissolved oxygen as an oxidant. The oxidase-like activity of BSA-Ag NCs was "switched-on" selectively in the presence of Hg(2+), which permitted a novel and facile colorimetric sensor for Hg(2+). As low as 25 nmol L(-1)Hg(2+) could be detected with a linear range from 80 nmol L(-1) to 50 mmol L(-1). In addition, the sensing strategy was also employed to detect DNA molecules. Hg(2+) is known to bind very strongly and specifically with two DNA thymine bases (T) to form thymine-Hg(2+)-thymine (T-Hg(2+)-T) base pairs. The hairpin-structure was disrupted and Hg(2+) ions were released after hybridization with the DNA target. By coupling the Hg(2+) switched-on the oxidase-mimicking activity of BSA-Ag NCs, we developed a novel label-free strategy for facile and fast colorimetric detection of DNA molecules. More important, target DNA can be detected as low as 10 nmol L(-1) with a linear range from 30 to 225 nmol L(-1). Compared with other methods, this method presents several advantages such as the independence of hydrogen peroxide, high sensitivity and good selectivity, avoiding any modification or immobilization of DNA, which holds a great potential of metal NCs for clinical application in biosensing and biotechnology.

A novel photoelectrochemical sensor based on photocathode of PbS quantum dots utilizing catalase mimetics of bio-bar-coded platinum nanoparticles/G-quadruplex/hemin for signal amplification.

Photocathode based on p-type PbS quantum dots (QDs) combing a novel signal amplification strategy utilizing catalase (CAT) mimetics was designed and utilized for sensitive photoelectrochemical (PEC) detection of DNA. The bio-bar-coded Pt nanoparticles (NPs)/G-quadruplex/hemin exhibited high CAT-like activity following the Michaelis-Menten model for decomposing H2O2 to water and oxygen, whose activity even slightly exceeded that of natural CAT. The bio-bar-code as a catalytic label was conjugated onto the surface of PbS QDs modified electrodes through the formed sandwich-type structure due to DNA hybridization. Oxygen in situ generated by the CAT mimetics of the bio-bar-code of Pt NPs/G-quadruplex/hemin acted as an efficient electron acceptor of illuminated PbS QDs, promoting charge separation and enhancing cathodic photocurrent. Under optimal conditions, the developed PEC biosensor for target DNA exhibited a dynamic range of 0.2pmol/L to 1.0nmol/L with a low detection limit of 0.08pmol/L. The high sensitivity of the method was resulted from the sensitive response of PbS QDs to oxygen and the highly efficient CAT-like catalytic activity of the bio-bar-coded Pt NPs/G-quadruplex/hemin.

Intrinsic enzyme mimicking activity of gold nanoclusters upon visible light triggering and its application for colorimetric trypsin detection.

In this research, a novel enzyme mimetics based on the photochemical property of gold nanoclusters was demonstrated. It was found that the bovine serum albumin (BSA) stabilized red or blue emitting gold nanoclusters (Au NCs) exhibited enzyme-like activity under visible light irradiation. The BSA-Au NCs had better stability against stringent conditions compared to natural enzyme. In addition, the photostimulated enzyme mimetics of BSA-Au NCs showed several unprecedented advantages over natural peroxidase or other existing alternatives based on nanomaterials, such as the independence of hydrogen peroxide on activity and the easily regulated activity by light irradiation. The mechanism of the photoresponsive enzyme-like activity of BSA-Au NCs was investigated. The photoactivated BSA-Au NCs was designed to develop a facile, cheap, and rapid colorimetric assay to detect trypsin through trypsin digestion of the protein template of BSA-stabilized Au NCs. The limit of detection for trypsin was 0.6 µg/mL, which was much lower than the average level of trypsin in patient's urine or serum.

An ultrasensitive and universal photoelectrochemical immunoassay based on enzyme mimetics enhanced signal amplification.

An ultrasensitive photoelectrochemical (PEC) immunoassay based on signal amplification by enzyme mimetics was fabricated for the detection of mouse IgG (as a model protein). The PEC immunosensor was constructed by a layer-by-layer assembly of poly (diallyldimethylammonium chloride) (PDDA), CdS quantum dots (QDs), primary antibody (Ab1, polyclonal goat antimouse IgG), and the antigen (Ag, mouse IgG) on an indium-tin oxide (ITO) electrode. Then, the secondary antibody (Ab2, polyclonal goat antimouse IgG) combined to a bio-bar-coded Pt nanoparticle(NP)-G-quadruplex/hemin probe was used for signal amplification. The bio-bar-coded Pt NP-G-quadruplex/hemin probe could catalyze the oxidation of hydroquinone (HQ) using H2O2 as an oxidant, demonstrating its intrinsic enzyme-like activity. High sensitivity for the target Ag was achieved by using the bio-bar-coded probe as signal amplifier due to its high catalytic activity, a competitive nonproductive absorption of hemin and the steric hindrance caused by the polymeric oxidation products of HQ. For most important, the oxidation product of HQ acted as an efficient electron acceptor of the illuminated CdS QDs. The target Ag could be detected from 0.01pg/mL to 1.0ng/mL with a low detection limit of 6.0fg/mL. The as-obtained immunosensor exhibited high sensitivity, good stability and acceptable reproducibility. This method might be attractive for clinical and biomedical applications.

A new approach to light up the application of semiconductor nanomaterials for photoelectrochemical biosensors: using self-operating photocathode as a highly selective enzyme sensor.

Due to the intrinsic hole oxidation reaction occurred on the photoanode surface, currently developed photoelectrochemical biosensors suffer from the interference from coexisting reductive species (acting as electron donor) and a novel design strategy of photoelectrode for photoelectrochemical detection is urgently required. In this paper, a self-operating photocathode based on CdS quantum dots sensitized three-dimensional (3D) nanoporous NiO was designed and created, which showed highly selective and reversible response to dissolved oxygen (acting as electron acceptor) in the electrolyte solution. Using glucose oxidase (GOD) as a biocatalyst, a novel photoelectrochemical sensor for glucose was developed. The commonly encountered interferents such as H2O2, ascorbic acid (AA), cysteine (Cys), dopamine (DA), etc., almost had no effect for the cathodic photocurrent of the 3D NiO/CdS electrode, though these substances were proved to greatly influence the photocurrent of photoanodes, which indicated greatly improved selectivity of the method. The method was applied to detect glucose in real samples including serum and glucose injections with satisfactory results. This study could provide a new train of thought on designing of self-operating photocathode in photoelectrochemical sensing, promoting the application of semiconductor nanomaterials in photoelectrochemistry.

In situ formation of p-n junction: a novel principle for photoelectrochemical sensor and its application for mercury(II) ion detection.

The discovery and development of photoelectrochemical sensors with novel principles are of great significance to realize sensitive and low-cost detection. In this paper, a new photoelectrochemial sensor based on the in situ formation of p-n junction was designed and used for the accurate determination of mercury(II) ions. Cysteine-capped ZnS quantum dots (QDs) was assembled on the surface of indium tin oxide (ITO) electrode based on the electrostatic interaction between Poly(diallyldimethylammonium chloride) (PDDA) and Cys-capped ZnS QDs. The in situ formation of HgS, a p-type semiconductor, on the surface of ZnS facilitated the charge carrier transport and promoted electron-hole separation, triggered an obviously enhanced anodic photocurrent of Cys-capped ZnS QDs. The formation of p-n junction was confirmed by P-N conductive type discriminator measurements and current-voltage (I-V) curves. The photoelectrochemical method was used for the sensing of trace mercuric (II) ions with a linear concentration of 0.01 to 10.0 µM and a detection limit of 4.6×10(-9)mol/L. It is expected that the present study can serve as a foundation to the application of p-n heterojunction to photoelectrochemical sensors and it might be easily extended to more exciting sensing systems by photoelectrochemistry.

Dual responsive enzyme mimicking activity of AgX (X=Cl, Br, I) nanoparticles and its application for cancer cell detection.

Chitosan (CS) modified silver halide (AgX, X=Cl, Br, I) (CS-AgX) nanoparticles (NPs) were found to possess dual responsive enzyme mimetic activities. In the presence of H2O2, they were able to oxidize various colorimertic dyes, namely, peroxidase-like activity. Upon photoactivation, CS-AgX NPs could also oxidize the typical substrates in the absence of H2O2. Taking CS-AgI as an example, it was found that the photostimulated enzyme mimetics of CS-AgI NPs showed several unprecedented advantages over natural peroxidase or other existing alternatives based on nanomaterials, such as excellent enzyme-like activity over a broad pH range (3.0-7.0), the independence of hydrogen peroxide on activity, the easily regulated activity by light irradiation, and the good reutilization without significant loss of catalytic activity. The mechanism of the dual responsive enzyme-like activity of CS-AgI was investigated. On the basis of these findings, the photoactivated CS-AgI was designed to develop a facile, cheap, rapid, and highly sensitive colorimetric assay to detect cancer cells. The detection limit of the method for MDA-MB-231 was estimated to be as low as 100 cells, which was much lower than that reported by the method using peroxidase mimetics based on nanomaterials. We believe that CS-AgX NPs with dual responsive enzyme-mimicking activity, especially the excellent photostimulated enzyme-like activity, may find widely potential applications in biosensors.

The pH-dependent interaction of silver nanoparticles and hydrogen peroxide: a new platform for visual detection of iodide with ultra-sensitivity.

Considering the significance and urgency for the recognition and sensing of anions specifically, especially those of biological relevance, herein, a simple and reliable colorimetric iodide sensor that based on pH-dependent interaction of silver nanoparticles (AgNPs) and H2O2 was developed. In acidic medium, AgNPs reacted with H2O2 to produce Ag(+) and powerful oxidizing species. The powerful oxidizing species could etch AgNPs seriously. While, iodide acted as an antioxidant could protect AgNPs from oxidation-etching by the powerful oxidizing species. In neutral and alkaline medium, the reaction of AgNPs and H2O2 mainly produce Ag(+). The existence of iodide could complex with Ag(+), forming AgI, which paved the way for aggregation of AgNPs. Based on the different responses of iodide to these different products of the reaction between H2O2 and AgNPs in solutions with different pH, iodide with concentrations down to 1 nM in acidic medium, 6 nM in neutral medium, and 100 nM in alkaline medium could be detected by naked-eye. More importantly, urinary iodide had been detected successfully. This simple and speedy method, which also exhibited remarkable selectivity and outstanding sensitivity, not only innovated the field of iodide recognition but also opened up a novel insight of the application of AgNPs.

Novel switchable sensor for phosphate based on the distance-dependant fluorescence coupling of cysteine-capped cadmium sulfide quantum dots and silver nanoparticles.

A novel switchable sensor was developed for the determination of phosphate based on Ce(3+) induced aggregation and phosphate triggered disaggregation of cysteine (Cys)-capped CdS quantum dots (QDs) and silver nanoparticles (AgNPs). The rare earth metal Ce(3+) could aggregate a mixture of QDs and AgNPs, which induced electron or energy transfer between CdS QDs and AgNPs and serious fluorescence quenching. However, phosphate dissociated the formed aggregation of CdS QDs and AgNPs, restoring the enhanced fluorescence of Cys-capped CdS triggered by AgNPs. Although, CdS QDs alone could also be used to detect phosphate through the aggregation-disaggregation mechanism adjusted by Ce(3+) and phosphate. It was found that the distance-dependent interaction between AgNPs and CdS QDs driven by Ce(3+) and phosphate could lead to enhanced quenching or enhancement of the fluorescence of Cys-capped CdS to form a more sensitive detection system for phosphate. The developed method was applied in the detection of phosphate in real water samples with acceptable and satisfactory results.

"Oxidative etching-aggregation" of silver nanoparticles by melamine and electron acceptors: an innovative route toward ultrasensitive and versatile functional colorimetric sensors.

An innovative and versatile functional colorimetric sensor for melamine (MA) and H(2)O(2) was developed with simplicity, excellent selectivity and ultrasensitivity. The detection mechanism was based on the "oxidative etching-aggregation" of silver nanoparticles (AgNPs) by the cooperation effect of MA and electron acceptors such as H(2)O(2), ozone or Fe(NO(3))(3). The detection limits of this method for MA could reach as low as 0.08 nM, 0.16 nM and 3 nM when H(2)O(2), ozone or Fe(NO(3))(3) was used as an electron acceptor, respectively. When using H(2)O(2) as a typical electron acceptor, the method enabled the detection of H(2)O(2) with a detection limit of 0.2 nM. This proposed method offered a new way to design MA and H(2)O(2) sensors and might be easily extended to detect other nucleophilic reagents and electron acceptors based on colorimetric sensors.

Enhanced fluorescence sensing of melamine based on thioglycolic acid-capped CdS quantum dots.

A sensitive and simple method for the determination of melamine (MA) was developed based on the fluorescence enhancement effect of MA for thioglycolic acid-capped (TGA-capped) CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 2.0 × 10(-9) to 5.0 × 10(-5)M. The detection limit was 1.0 × 10(-9)M, which was much lower than the safety limit (2.5 ppm in USA and the UK; 1 ppm for infant formula in China). The solution pH, the adding sequence of the buffer solution and MA and surface modifiers of CdS QDs greatly influenced the enhancement extent of MA for CdS QDs. The fluorescence enhancement was attributed to the surface passivation of the surface states of QDs by amine group of MA. The method was applied to detect MA in raw milk with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

Ultrasensitive and dual functional colorimetric sensors for mercury (II) ions and hydrogen peroxide based on catalytic reduction property of silver nanoparticles.

The method provides an innovative dual functional sensors for mercury (II) ions and hydrogen peroxide. The addition of H(2)O(2) to the mixture of silver nanoparticles (AgNPs) and Hg(2+) induced color changes of the solution within several seconds even at 2.0 nM Hg(2+). Other metallic ions could not induce color change even at 10 µM. Of importance, this probe was not only successfully applied to detect Hg(2+), but also it could be used to sense H(2)O(2) at a concentration as low as 50 nM (by naked-eye). The outstanding sensitivity and selectivity property for Hg(2+) and H(2)O(2) resulted from the AgNPs mediated reduction of Hg(2+) to elementary Hg in the presence of H(2)O(2), causing the aggregation and colorimetric response of AgNPs. This sensitive and selective colorimetric assay opens up a fresh insight of development facile and fast detection methods for metal ions and biomolecules using the special catalytic reactivity of AgNPs.

Metal ion (silver, cadmium and zinc ions) modified CdS quantum dots for ultrasensitive copper ion sensing.

Metal ion (Ag(+), Cd(2+), Zn(2+)) modified CdS quantum dots (QDs) were synthesized and used for Cu(2+) sensing. Modification by these metal ions could enhance the PL intensity of CdS QDs with the extent of the PL enhancement being related to the concentration of the metal ions. Different metal ion (Ag(+), Cd(2+), Zn(2+)) modified CdS QDs also showed different analytical characteristics for Cu(2+) sensing. In particular, Ag( + ) modified CdS QDs showed greatly enhanced sensitivity for Cu(2+) determination than did the unmodified CdS QDs. A limit of detection (LOD) of 2.0 × 10(-10) M was obtained for Ag(+) modified CdS QDs, which is the lowest LOD obtained using QDs as fluorescence probes for Cu(2+) sensing. This study demonstrates the important role of surface state of QDs in fluorescence sensing.

Ultrasensitive cysteine sensing using citrate-capped CdS quantum dots.

The importance of cysteine (Cys) in biological systems has stimulated a great deal of efforts in the development of analytical methods for the determination of this amino acid. In this work, a novel fluorescent probe for Cys based on citrate (Cit)-capped CdS quantum dots (QDs) is reported. The Cit-capped CdS QDs fluorescent probe offers good sensitivity and selectivity for detecting Cys. A good linear relationship was obtained from 1.0 × 10(-8)mol L(-1) to 5.0 × 10(-5)mol L(-1) for Cys. The detection limit was calculated as 5.4 × 10(-9)mol L(-1). The proposed method was applied to detect Cys in human urine samples, which showed satisfactory results. This assay is based on both the lability of Cit and the strong affinity of thiols to the surface of CdS QDs. The addition of Cys improved the passivation of the surface traps of CdS QDs and enhanced the fluorescence intensity.

[Novel ionic liquid as solvent for preconcentration of trace lead in dialysis fluids and its determination by graphite furnace atomic absorption spectrometry].

A novel room temperature ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate was designed and synthesized, and was applied to the preconcentration of ultra trace lead in a relatively large volume of dialysis fluids (such as 1 000 mL or bigger). In the present work, dithizone was employed as chelator to form a neutral lead- dithizone complex, and the ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate was used to displace CCl4 as solvent for liquid/liquid extraction of lead complex. The ionic liquid was collected and the lead (II) was back-extracted into aqueous solution by adding nitric acid solution, and the above solution was directly applied to determine lead in the dialysis fluids by graphite furnace atomic absorption spectrometry. Experiments indicated that the proposed extraction system is superior over other systems in which organic solvent such as CCl4 or classical room temperature ionic liquid1-butyl-3-methylimidazolium hexafluorophosphate was selected as extraction medium, and its extraction efficiency of once extraction and enrichment factor of lead was more than 99% and 200 times, respectively. The preconcentration combined with graphite furnace atomic absorption spectrometry has been applied to the determination of trace lead in dialysis fluid samples with satisfactory results.

[Study on the application of methybenzeneazosalicylfluorone to spectrophotometric determination of microelement molybdenum modality distributions in soy hydrolysate hydrolyzed by enzymes].

A new method has been developed for spectrophotometric determination of molybdenum modality distributions in soy hydrolysate hydrolyzed by enzymes, based on the study on the color reaction of methybenzeneazosalicylfluorone (abbreviated as MBASF) with molybdenum (VI). In hydrochloric acid medium, MBASF reacts with molybdenum (VI) sensitively to form a stable red complex, its apparent molar absorptivity is 1.54 L x mol(-1) x cm(-1), and 0-12 microg of molybdenum obeys Beer's law in 25 mL of solution. Besides normal metal ions, protein, peptide and amino acid also have high tolerance limits. Soy hydrolysate hydrolyzed by enzyme (A) was precipitated at its isoelectric point, and the filtrate (B) was obtained. Subsequently, B was transferred to the chromatogram column with D301R resin. The column was purged by using 20 mL of HAc-NaAc (pH 3.6) and NH4Cl-NH3 x H2O buffer solution(pH 9) orderly and the effluent solutions C and D were obtained. A, B, C and D solutions were used for the spectrophotometric determination of total molybdenum, hydrolyzed molybdenum, chelated molybdenum by peptide or amino acid, and dissociative molybdenum, respectively.