Advancements in Preprocessing and Analysis of Nitrite and Nitrate since 2010 in Biological Samples: A Review.

As a substance present in organisms, nitrite is a metabolite of nitric oxide and can also be ingested. Nitrate is the metabolite of nitrite. Therefore, it is necessary to measure it quickly, easily and accurately to evaluate the health status of humans. Although there have been several reviews on analytical methods for non-biological samples, there have been no reviews focused on both sample preparation and analytical methods for biological samples. First, rapid and accurate nitrite measurement has significant effects on human health. Second, the detection of nitrite in biological samples is problematic due to its very low concentration and matrix interferences. Therefore, the pretreatment plus measuring methods for nitrite and nitrate obtained from biological samples since 2010 are summarized in the present review, and their prospects for the future are proposed. The treatment methods include liquid-liquid microextraction, various derivatization reactions, liquid-liquid extraction, protein precipitation, solid phase extraction, and cloud point extraction. Analytical methods include spectroscopic methods, paper-based analytical devices, ion chromatography, liquid chromatography, gas chromatography-mass spectrometry, electrochemical methods, liquid chromatography-mass spectrometry and capillary electrophoresis. Derivatization reagents with rapid quantitative reactions and advanced extraction methods with high enrichment efficiency are also included. Nitrate and nitrate should be determined at the same time by the same analytical method. In addition, much exploration has been performed on formulating fast testing through microfluidic technology. In this review, the newest developments in nitrite and nitrate processing are a focus in addition to novel techniques employed in such analyses.

When judging what you know changes what you really know: Soliciting metamemory judgments reactively enhances children's learning.

Recent studies established that making concurrent judgments of learning (JOLs) can significantly alter (typically enhance) memory itself-a reactivity effect. The current study recruited 190 Chinese children (Mage  = 8.68 years; 101 female) in 2020 and 2021 to explore the reactivity effect on children's learning, its developmental trajectory and associated metacognitive awareness. The results showed that making JOLs significantly enhanced retention for students in Grades 1, 3, and 5, with Cohen's ds ranging from 0.40 to 1.33. Grade 5 students exhibited a larger reactivity effect than Grade 1 and 3 students. Children's metacognitive appreciation of the effect was weak. Firsthand experience of the reactivity effect, induced by taking a memory test, enhanced their awareness and calibrated their judgment accuracy.

Physicochemical, rheological, antioxidant and immunological properties of four novel non-inulin (poly)saccharides from Asparagus cochinchinensis.

The impacts of four extraction techniques, including hot water, ultrasonic-assisted, complex enzyme-assisted and acid-assisted methods, on the morphological, physicochemical properties and bioactivities of Asparagus cochinchinensis (poly)saccharides (EACP, WACP, UACP, and AACP) were investigated and compared. The four samples were mainly composed of glucose, fructose, and galactose with molar ratios of 50.8:22.7:4.4 for WACP, 53.9:26.0:5.3 for UACP, 35.6:14.1:21.4 for AACP and 45.0:15.6:9.0 for EACP, respectively. The rheological result showed that ACPs were non-Newtonian fluids. EACP with high purity (97.65 %) had good DPPH, O2- and ABTS+ radical scavenging activities, and significantly promoted the proliferation of the RAW264.7 cells at low concentration. UACP had good Fe2+ chelating ability, radical (DPPH, O2- and OH) scavenging activities, which might be attributed to the existence of triple-helix structure. AACP had high yield, molecular weight (17,477.2 Da), high crystallinity (23.33 %), and good radical (OH and ABTS+) scavenging activities. All four significantly stimulated the transcript expression levels of TNF-α, IL-1ß and IL-6, as determined by RT-PCR. These results suggest that the exploitation and utilization of non-inulin (poly)saccharides extracted by ultrasonic-assisted, complex enzyme-assisted and acid-assisted extraction methods are potentially valuable as effective and natural immune adjuvants and antioxidants.

Preparation and potential antitumor activity of alginate oligosaccharides degraded by alginate lyase from Cobetia marina.

It is of great significance to develop marine resources and study its potential biological activity by using alginate lyase produced by marine psychrophilic bacteria. In the previous study, a new marine psychrophilic bacterium (Cobetia marina HQZ08) was screened from the growth area of Laminaria japonica, and it was found that the strain could efficiently produce alginate-degrading enzyme (Aly30). In this paper, the ability of Aly30 to degrade alginate was optimized and the optimal degradation conditions were obtained. It was found that the main degradation product of alginate oligosaccharides was trisaccharide. In vitro cell experiments showed that the antitumor activity of low molecular weight alginate oligosaccharides was better than that of high molecular weight alginate oligosaccharides. In summary, Aly30 had the potential to produce alginate oligosaccharides with low degree of polymerization and antitumor activity, which provided a reference for the enzymatic preparation and application of alginate oligosaccharides.

Gold nanocluster-confined covalent organic frameworks as bifunctional probes for electrochemiluminescence and colorimetric dual-response sensing of Pb2.

The development of bifunctional signal probes based on a single component is highly desirable for sensitive and simple dual-mode detection of Pb2+. Here, novel gold nanocluster-confined covalent organic frameworks (AuNCs@COFs) were fabricated as a bisignal generator to enable electrochemiluminescence (ECL) and colorimetric dual-response sensing. AuNCs with both intrinsic ECL and peroxidase-like activity were confined into the ultrasmall pores of the COFs via an in situ growth method. On the one hand, the space-confinement effect of the COFs closed the ligand motion-induced nonradiative transition channels of the AuNCs. As a result, the AuNCs@COFs exhibited a 3.3-fold enhancement in anodic ECL efficiency compared to the solid-state aggregated AuNCs using triethylamine as the coreactant. On the other hand, due to the outstanding spatial dispersibility of the AuNCs in the structurally ordered COFs, a high density of active catalytic sites and accelerated electron transfer were obtained, leading to the promotion of the enzyme-like catalytic capacity of the composite. To validate its practical applicability, a Pb2+-triggered dual-response sensing system was proposed based on the aptamer-regulated ECL and peroxidase-like activity of the AuNCs@COFs. Sensitive determinations down to 7.9 pM for the ECL mode and 0.56 nM for the colorimetric mode were obtained. This work provides an approach for designing single element-based bifunctional signal probes for dual-mode detection of Pb2+.

Label-free Hg(II) electrochemiluminescence sensor based on silica nanoparticles doped with a self-enhanced Ru(bpy)32+-carbon nitride quantum dot luminophore.

Herein, a label-free, self-enhanced electrochemiluminescence (ECL) sensing strategy for divalent mercury (Hg(II)) detection was presented. First, a novel self-enhanced ECL luminophore was prepared by combining the ECL reagent tris(2, 2'-bipyridyl) dichlororuthenium(II) hexahydrate (Ru(bpy)32+) and its co-reactant carbon nitride quantum dots (CNQDs) via electrostatic interactions. In contrast to traditional ECL systems where the emitter and its co-reactant underwent an intermolecular reaction, the self-enhanced ECL system exhibited a shortened electron-transfer distance and enhanced luminous efficiency because the electrons transferred from CNQDs to oxidized Ru(bpy)32+ via an intramolecular pathway. Furthermore, the as-prepared self-enhanced ECL material was encapsulated in silica (SiO2) nanoparticles to generate a Ru-QDs@SiO2 luminophore. Based on the different affinity of Ru-QDs@SiO2 nanoparticles for single-stranded DNA (ssDNA) and Hg(II)-triggered double-stranded DNA (dsDNA), a label-free ECL biosensor for Hg(II) detection was developed as follows: in the absence of Hg(II), ssDNA was adsorbed on Ru-QDs@SiO2 surface via hydrogen bond, electrostatic, and hydrophobic interaction. Thus, quenched ECL signal was observed. On the contrary, in the presence of Hg(II), stable dsDNA was formed and carried the ssDNA separating from Ru-QDs@SiO2 surface, resulting in most of Ru-QDs@SiO2 existing in their free state. Therefore, a recovered ECL intensity was obtained. On this basis, Hg(II) was measured by the proposed method in the range of 0.1 nM-10 µM, with a detection limit of 33 pM. Finally, Hg(II) spiked in water samples was measured to evaluate the practicality of the fabricated biosensor.

An ultra-high-sensitivity electrochemiluminescence aptasensor for Pb2+ detection based on the synergistic signal-amplification strategy of quencher abscission and G-quadruplex generation.

Signal amplification provides an effective way to improve detection performance. Herein, an ultrasensitive electrochemiluminescence (ECL) aptasensor for Pb2+ detection was developed based on a dual signal-amplification strategy of the abscission of a quencher and the generation of a G-quadruplex by one-step and simultaneous way. Nitrogen-doped carbon quantum dots linked with complementary DNA (cDNA-NCQDs) at the sensing interface was applied as the quencher of a tris(4,4'-dicarboxylic acid-2,2'-bipyridyl)ruthenium(II) (Ru(dcbpy)32+)/tripropylamine system to minimize the ECL signal due to the intermolecular hydrogen bond-induced energy-transfer process. Upon the addition of Pb2+, its specific binding with the aptamer triggered the abscission of cDNA-NCQDs, accompanied by the formation of G-quadruplex on the surface of the electrode, both of which amplified the intensity of the light emission. The ECL amplification efficiency induced by the above two mechanisms (78.6%) was valuably greater than that of their sum value (69.3%). This synergistic effect resulted in high detection sensitivity of the ECL aptasensor, which allowed to thereby obtain Pb2+ measurements in the range of 1 fM - 10 nM with an ultra-low detection limit of 0.19 fM. The Pb2+-mediated synergistic signal-amplification ECL strategy can provide a new approach for integrating various amplification strategies.

An intermolecular hydrogen-bond-induced quench-type Ru(dcbpy)32+/TPA electrochemiluminescence system by nitrogen-doped carbon quantum dots.

Here, we show that nitrogen-doped carbon quantum dots (NCQDs) strongly inhibits the anodic electrochemiluminescence (ECL) signal of a tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) (Ru(dcbpy)32+)/tripropylamine (TPA) aqueous system. To determine the ECL-quenching mechanism, we used photoluminescence spectroscopy, UV-Visible absorption spectroscopy and dynamic simulation technology. Quenching of the ECL signal of Ru(dcbpy)32+/TPA by NCQDs was predominantly attributed to the interaction between Ru(dcbpy)32+ and NCQDs rather than that between TPA and NCQDs. Specifically, when Ru(dcbpy)32+ and NCQDs were in aqueous solution together, the carboxyl (-COOH) groups of Ru(dcbpy)32+ were in contact with oxygen- and nitrogen-containing groups on the surface of NCQDs and formed intermolecular hydrogen bonds. This process involved energy transfer from the excited-state Ru(dcbpy)32+ to the intermolecular hydrogen bonds, thus resulting in a decrease in the Ru(dcbpy)32+ ECL signal. On this basis, a quenching-type ECL sensor for the quantification of NCQDs was fabricated. The sensor had a wide linear range and an estimated detection limit of 0.0012 mg mL-1, as well as excellent stability and selectivity. Satisfactory recoveries of 97.0-99.5% were obtained using the ECL sensor to quantify NCQDs in tap water. NCQDs could potentially be used as a quenching probe of Ru(dcbpy)32+ to construct various biosensors with widespread applications in the sensing field.