Polynucleotide kinase (PNK) that phosphorylates 5'-hydroxyl termini of nucleic acids plays a vital role in DNA replication, recombination, and repair and is regarded as both a critical biomarker and therapeutic target. PNK analysis is based on conversion of 5'-hydroxyl group to 5'-phosphate group catalyzed by the enzyme, which is challenging to be optically detected and generally requires additional enzymes and steps for signal transduction. Besides complicating the assay, it is hard to keep each step with their optimal reaction condition and masks the heterogeneous characteristics of PNK. Herein, we propose a straightforward strategy for visualized detection of PNK. In this strategy, PNK-catalyzed DNA phosphorylation is demonstrated to be able to enhance the overhang binding between strands on gold nanoparticles, which cross-links DNA-modified gold nanoparticles (AuNPs) into network aggregates. The tiny terminal group conversion is thus transduced into bulk nanoparticle aggregation and shows visible color change. It is found that either one strand phosphorylation can stick the duplex and leads to AuNP cross-linking, which influences nanoparticle dispersion state and obtains a high sensitivity comparable to fluorescent or electrochemical methods. The strategy also shows a high specificity toward PNK and can be used for PNK inhibitor analysis. Furthermore, since the aggregation of AuNPs leads to increased light scattering, intracellular imaging of PNK is realized with dark field microscopy by cell endocytosis of DNA-modified AuNPs, showing bright scattering nanoparticle aggregates inside cells. The work proposes a new PNK detection principle and provides a straightforward, convenient, and visual way for PNK analysis.

Lateral flow assay is a strip-based method, in which the loaded sample can flow across the strip autonomously and induce test line and/or control line coloration for visual determination of target of interest. It has the advantages of portable assay, easy operation, and no analytical instruments. A universally applicable way is the target-sandwiched linking of reporter elements to capture units on the test line. However, a common concern therein is the possibility to generate false-positive signals, which can result from either the high similarity of analogues to target or the residue interaction between reporter elements and capture units in the absence of target. Herein, we propose a second flowing-type lateral flow assay, by which the second flow is utilized to test and correct the result of first flow. The test line that originally develops color during the first flow will retain color if target is indeed present while get discolored if target is absent, after the second flowing of designed displacing strands, to achieve a high-fidelity detection. We have demonstrated the discrimination of single base mutation in a 31-base length DNA oligonucleotide, as well as the differentiation of low concentration of adenosine triphosphate (ATP) from background interference by the second flowing-type lateral flow assay, both of which are prone to misjudging by false-positive signal in the one-time flowing. The strategy can also identify muted sites or base types that are unknown a priori and restricted to the region complementary to the displacing strand. The second flowing-type lateral flow assay provides an effective and feasible way to ensure detection accuracy and reliability in the universally adopted target-sandwiched lateral flow detection.

Polynucleotide kinase (PNK) that phosphorylates 5 '-hydroxyl termini of nucleic acids plays a vital role in DNA replication, recombination, and repair and is regarded as both a critical biomarker and therapeutic target. PNK analysis is based on conversion of 5 '-hydroxyl group to 5 '-phosphate group catalyzed by the enzyme, which is challenging to be optically detected and generally requires additional enzymes and steps for signal transduction. Besides complicating the assay, it is hard to keep each step with their optimal reaction condition and masks the heterogeneous characteristics of PNK. Herein, we propose a straightforward strategy for visualized detection of PNK. In this strategy, PNK-catalyzed DNA phosphorylation is demonstrated to be able to enhance the overhang binding between strands on gold nanoparticles, which cross-links DNA-modified gold nanoparticles (AuNPs) into network aggregates. The tiny terminal group conversion is thus transduced into bulk nanoparticle aggregation and shows visible color change. It is found that either one strand phosphorylation can stick the duplex and leads to AuNP cross-linking, which influences nanoparticle dispersion state and obtains a high sensitivity comparable to fluorescent or electrochemical methods. The strategy also shows a high specificity toward PNK and can be used for PNK inhibitor analysis. Furthermore, since the aggregation of AuNPs leads to increased light scattering, intracellular imaging of PNK is realized with dark field microscopy by cell endocytosis of DNA-modified AuNPs, showing bright scattering nanoparticle aggregates inside cells. The work proposes a new PNK detection principle and provides a straightforward, convenient, and visual way for PNK analysis.

Lateral flow assay owns advantages of easy operation, visual detection, and portable use. However, since the strip fabrication requires specific nanomaterial modification, zones pretreating/spraying, and particular capture unit immobilization, the as-prepared strip usually can detect just one type of target. To detect a new target, nanomaterial remodification and strip refabrication are needed, which is laborious, costly, and limited by access to the strip device. Here, we propose a DNA multiway junction based lateral flow assay facing different types of targets. Two assistant strands, named α and β, and a molecular beacon (MB) are designed, so as to form a DNA four-way junction with DNA/RNA nucleic acids or to a form DNA three-way junction with small molecules, proteins, and enzymes. The DNA multiway junction acts as a bridging complex to link DNA-modified gold nanoparticles on the test zone for coloration. We demonstrate the as-prepared lateral flow strip for detection of HBV viral DNA fragment, microRNA, ATP, thrombin, and terminal deoxynucleotidyl transferase (TdT). The DNA multiway junction based lateral flow assay provides a versatile, flexible, convenient, and cost-effective technique for visual detection of targets of interest.

Here, we design triplex DNA-modified gold nanoparticles that respond to a tunable pH range. Homopyrimidine strand-modified gold nanoparticles and homopurine/homopyrimidine duplexes are utilized in the system. Upon acidification, the duplexes bind to gold nanoparticle-conjugated strands through Watson-Crick and Hoogsteen base pairing, forming triplex DNA with blunt ends on the nanoparticle. The modified DNA outer layer generates base stacking interaction during gold nanoparticle collision, forming aggregate networks and inducing color change. The responding pH range can be tuned by varying the A/T proportion. Its applications as an accurate indicator in acid-base titration, for visual determination of acid rain, and in colorimetric detection of 3-nitropropionic acid that exists in deteriorated sugar cane are demonstrated.

The lateral flow assay is a strip-based analytical method for the portable and convenient detection of analytes of interest. It has the advantages of visual observation, autonomous sample flow, fast coloration time, minimal tedious operation procedures, and reliance on specialized instruments. However, the rough surface of the nitrocellulose membrane renders it difficult for the immobilized nucleic acids to remain in an ordered arrangement, and the immobilized nucleic acids are also liable to be digested in a complex matrix, inducing limited sensitivity and anti-interference. In this work, we demonstrate that the decoration of DNA nanostructures on lateral flow strips can improve assay sensitivity and anti-interference in comparison with commonly studied single-stranded DNA-disposed strips. DNA nanostructures enable probes to be more orderly and arranged on the strip and provide protection. Using adenosine 5 '-triphosphate (ATP) as an analyte, a DNA tetrahedron reformative lateral flow strip has increased sensitivity and improved reliability in detection. The DNA nanostructure-decorated lateral flow strip is further successfully applied for ATP detection in real samples, such as bacterium testing and tableware cleanliness checking, by detection of the ATP content therein.

All of the commercialized electrochemiluminescence (ECL) immunoassays are automatically conducted at +1.40 V (vs Ag/AgCl) in the coreactant route. To alleviate the exogenous effect of coreactants and simplify the operation procedures, herein, a sulfur-vacancy-involved and free electron strategy is proposed to exploit Au nanoclusters (NCs) as anodic electrochemiluminophores and perform a coreactant-free immunoassay. The deficient coordination between the sulfhydryl of Met and the Au core might induce the departure of partial S atoms and enable Met-capped AuNCs (Met-AuNCs) with a sulfur-vacancy-involved electron-rich nature. The electron-rich nature tends to endow Met-AuNCs with unpaired endogenous free electrons, which can directly combine exogenous holes for light emitting. Coreactant-free ECL at around +0.86 V is consequently and conveniently achieved by merely oxidizing Met-AuNCs at the anode. The coreactant-free ECL is qualified to determine human carcinoembryonic antigen from 10 to 5000 pg/mL with a limit of detection of 5 pg/mL. Electron paramagnetic resonance provides clear evidence that endogenous free electrons within Met-AuNCs play an important role in the generation of coreactant-free ECL. This sulfur-vacancy-involved and free electron strategy is promising for designing nanoelectrochemiluminophores with improved immunoassay performance.

Parkinson’s disease (PD), the second most common neurodegenerative disorder, is typically diagnosed based on clinical observation of motor symptoms such as resting tremor, rigidity, and bradykinesia. This underscores the urgent need for a diagnostic tool capable of detecting PD at an earlier stage. Since the appearance of α-synuclein oligomer in saliva occurs earlier than the onset of motor symptoms, we introduce a lateral flow strip utilizing split aptamer to detect α-synuclein oligomer in the saliva of PD patients. When α-synuclein oligomer are present, they facilitate the reassembly of split aptamer, creating an “aptamer-α-synuclein oligomer-aptamer” sandwich structure. This assembly allows DNA-modified gold nanoparticles to be captured on the test line of the strip, producing a visible red band. Through careful optimization of the strip’s operational conditions, this system exhibited a linear relationship within the range 0–10 µmol/L and a LOD of 62.72 nmol/L. Quantitative analysis of the results from PD patients showed positive outcomes in 14 out of 20 cases. Compared to existing detection methods, this approach offers several advantages, including visual results, short detection time, ease of use, low cost, portability and no requirement for complex sample pretreatment. These features make it a promising tool for the early diagnosis and visual assessment of PD.

The copper(Ⅱ)-ammonia coordination ion represents a quintessential model for understanding the coordination equilibrium and distribution characteristics of coordination compounds in the teaching of analytical chemistry. Current textbooks, however, often limit their scope to providing stability constants for select copper-ammonia coordination ions, without delving into the correlation between their coordination numbers and stability. This study leverages density functional theory to firstly establish a connection between the stability of copper-ammonia coordination ions and their coordination numbers, achieved through structural optimization. Subsequently, it offers a qualitative interpretation by examining the molecule spatial configuration, shedding light on the fundamental nature of these structures. This research not only enhances the effectiveness of pedagogical approaches, but also cultivates students' interest in the application of the theoretical calculations within the realm of analytical chemistry.

Different types of pathogenic viruses that have common transmission path can be co-infected, inducing distinct disease procession in comparison to that infection of one. Also, in the post COVID-19 time, more types of respiratory infectious virus are becoming prevalent and are concurrent. Those bring an urgent need for detection of co-existing viruses. Here, we propose a visualized lateral flow assay for logic determination of co-existing viral RNA fragments. In the presence of specific viral RNA inputs, DNAzyme is de-blocked according to defined logic, and catalyzes the hydrolysis of hairpin-structural substrate. One of cleaved substrates contains DNAzyme domain to realize dual signal amplification, which obtains copious of the other cleaved substrates. The cleaved substrates act as linking strands for bridging DNA-modified gold nanoparticles onto lateral flow strip to induce coloration on test line. "AND", "OR" and "INHIBIT" controlled lateral flow assays are respectively demonstrated for co-existing viral RNA detection, and the visual results can be obtained by the same kind of prepared strip, without need of re-fabricating strips according to logic systems. The work provides a flexible, convenient, visual and logic-processing strategy for simultaneous analysis of co-existing viruses.

Here, we report a DNA tetrahedron dimer for dual membrane protein logic recognition and interaction inhibition. The DNA tetrahedron dimer not only detects dual proteins that are both overexpressed on target cells in "AND" logic, but also inhibits protein interaction by steric hindrance to suppress cell proliferation, offering new insights for cancer cell diagnosis and treatment.

Hybridization chain reaction (HCR) is a powerful enzyme-free nucleic acid amplification strategy. Triggered by an initiator strand, it yields nicked double helices analogous to alternating copolymers. However, there is no effective way to regulate the HCR reaction, and the most apparent phenomenon is the uncontrollable polymerization of product after introducing an initiator. Here we explore controlling the depth of the HCR reaction by extended dangling ends on hairpin monomers and report that sequence length, nucleotide composition, and secondary structure can alter HCR polymerization and can be utilized for the desired regulation. Interaction dynamics between initiator and hairpin monomers simulated by oxDNA are in good accordance with experimental results. Such a controlling effect can be utilized for new analytical applications that HCR cannot previously achieve, such as analyzing strand-extension enzymes and identifying short-sequence structures. The finding provides a concise but effective way for controlling the depth of HCR reaction and opens the application scope of HCR to more fields.

Energy drinks produce various health effects.Adjusting the composition and content of the natural nutrients in drinks can enable them to meet the nutritional needs of special groups of people.The quality of ingredients in beverages is directly related to the health of the people that consume them,and it is also an important part of the national food quality monitoring work.Based on the instrumental analysis experimental course of the School of Chemistry and Chemical Engineering of Shandong University,students independently designed experimental plans while teachers reviewed,guided,and supervised them.Their plans,which were closely associated with practical problems related to health,aimed to strengthen and expand the significance and application value of experimental learning.With the help of atomic absorption spectroscopy,they determined the zinc/sodium/potassium ion contents in commercially available energy drinks.The determined contents were tested and compared with the reference content marked on the package to determine whether there was any food quality problem with the drinks.The experiment conducted by the students completely supported their subjective initiative,enabling them to strengthen their theoretical knowledge learning,improve their practical ability,and deepen their understanding and application of atomic absorption spectroscopy in practice.This experiment fully reflected that theory and practice informed each other and allowed students to flexibly exploit the knowledge they gained in the course to solve practical problems,enabling them to intimately experience the close connection between life and chemistry.

In this technical note, we report an easy-to-produce,reverse-transcription-free,and protein-enzyme-free lateral flow assay for detection of viralRNA fragments by taking SARS-CoV-2 ORF1ab and N as target models.Catalytic hairpin assembly is utilized for dual RNA fragment orthogonalreaction to generate copious amounts of opened hairpin duplexes, whichbridge DNA-modified gold nanoparticles and capture strands on thestrip to induce coloration. The dual RNA fragments are simultaneouslyvisualized during one time of sample flow, and single-base-mismatchednontarget sequences can be differentiated. The test strip can be flexiblyadapted to detect evolutional SARS-CoV-2 variants such as Delta andOmicron. It also shows potential in visually detecting long-sequencevirus simulants and achieves a sensitivity comparable to that of RT-qPCRby incorporation with upstream sample amplification. The lateral flowassay should offer a convenient and reliable technique for viral nucleicacid detection.

DNA-based nanostructure is emerging as a promising tool for cell identification and regulation. Here we engineer an allosteric DNA triangular prism that responds to target cells with a folding behavior. It not only outputs signal via structural change that can avoid DNA nanostructure degradation-caused false positives, but also shows a fast migration inside cells via its folded structure that obtains a rapid regulation. The DNA prism simultaneously recognizes membrane receptors of human epidermal growth factor receptor 2 (HER2) and mucin 1 oncoprotein (MUC1), through the blocked aptamer unlocking and inner-structure strand displacement. Then the ipsilateral sides in the two triangle faces become single-stranded and form hairpin, forcing the DNA prism to be folded. The donor and acceptor fluorophores get close to each other and fluorescence resonance energy transfer is greatly enhanced. The folded DNA prism is further taken up by cells via HER2-mediated endocytosis, showing a faster arrival in lysosomes and leading to more rapid degradation of HER2 when compared with the unfolded prism structure. The folded DNA prism results in the reduction of cell motility and induction of cell apoptosis. Such an allosteric DNA nanostructure may offer new strategies for cancer cell diagnosis and treatment.

Acid-base titration is the most basic experiment in analytical chemistry.The titration curve reflects the whole process of neutralization reaction and is very important to understand acid-base titration.Based on three basic hypotheses, the chemical equilibrium, electroneutrality principle and mass balance, we established mathematical model between ionization degree and pH as well as titration percentage by keeping one parameter unchanged and the other two changed at the initial point.In addition, we recovered the acid-base titration curve by performing mathematical analysis and derivatization of the function.Through the analysis of two initial conditions in mathematical formula and the effects on the function, the quantitative validation on interpretations was introduced for reactions of different concentrations and strength of acids in titrations described in traditional teaching materials.With theoretical expansion of titration curves, we proposed a possible method for weak acid titration.

Deferasirox (DEF) is essential for patients with thalassemia requiring long-term transfusion therapy. Tigecycline (TIGE) is a first-line drug for the clinical treatment of complex, severe bacterial infections. The two drugs can be coordinated to treat Pseudomonas aeruginosa infections. Easy and efficient techniques for monitoring these two drugs in biological samples are few. Metal-organic framework (Zn-MOF) prepared from zinc nitrate hexahydrate and dithioglycolic acid has a flower structure. Interestingly, Zn-MOF can cause DEF to aggregate on it and induce DEF luminescence. The principle may be that Zn-MOF limits the vibration and rotation of DEF to avoid its nonradiative jump, which triggers aggregation-induced emission (AIE) and exhibits intense fluorescence. Further investigation revealed that TIGE could decompose Zn-MOF, thus alleviating the inhibitory effect of Zn-MOF on DEF and reducing the fluorescence intensity of DEF@Zn-MOF. A DEF/TIGE detection biosensor was created based on the fluorescence "turn-on" effect of Zn-MOF on DEF and the fluorescence "turn-off" effect of TIGE on DEF@Zn-MOF. The proposed technique was subsequently used to identify DEF/TIGE levels in pharmaceuticals and human plasma. The mean values for the percentage of the labeled amount of DEF/TIGE in DEF dispersible tablets/TIGE injection were 104.5 and 104.9%, respectively. The detection limits for the fluorescence detection of DEF and TIGE were 3.6 and 1.2 nM, respectively. This fluorescence assay is the first application of MOF to the simultaneous detection of DEF and TIGE and has the advantages of rapid sensitivity and high selectivity, providing a new strategy for drug detection.

Deferasirox (DEF) is essential for patients with thalassemia requiring long-term transfusion therapy. Tigecycline (TIGE) is a first-line drug for the clinical treatment of complex, severe bacterial infections. Easy and efficient techniques for monitoring these two drugs in biological samples are few. Metal–organic framework (Zn-MOF) prepared from zinc nitrate hexahydrate and dithioglycolic acid has a flower structure. Interestingly, Zn-MOF can cause DEF to aggregate on it and induce DEF luminescence. The principle may be that Zn-MOF limits the vibration and rotation of DEF to avoid its nonradiative jump, which triggers aggregation-induced emission (AIE) and exhibits intense fluorescence. Further investigation revealed that TIGE could decompose Zn-MOF, thus alleviating the inhibitory effect of Zn-MOF on DEF and reducing the fluorescence intensity of DEF@Zn-MOF. A DEF/TIGE detection biosensor was created based on the fluorescence "turn-on" effect of Zn-MOF on DEF and the fluorescence "turn-off" effect of TIGE on DEF@Zn-MOF. The proposed technique was subsequently used to identify DEF/TIGE levels in pharmaceuticals and human plasma. The recovery rates were 104.32%–104.64% for DEF dispersible and 102.4%–106.5% for TIGE injection The detection limits for the fluorescence detection of DEF and TIGE were 3.6 and 1.2 nM, respectively. This fluorescence assay is the first application of MOF to the simultaneous detection of DEF and TIGE and has the advantages of rapid sensitivity and high selectivity, providing a new strategy for drug detection.

: In view of the developing trend in the field and course characteristics of instrumental analysis, we analyzed the problems existing in its instruction in recent years. To solve these problems, ideas for reforming the content, teaching mode, examination, and evaluation standards are proposed. By improving and updating the theoretical content of modern instrumental analytical chemistry and promoting quality of teaching, students can master the basics to excel professionally. Simultaneously, ideological and political elements should be integrated into the content to comprehend the educational function of professional courses.

Timely and accurate detection of virus is crucial for preventing spread of disease and early treatment of the infected cases. Herein we design an integrated logic-operated three-dimensional DNA walker for colorimetric detection of viral RNA fragments, by taking SARS-CoV-2 as an example. The DNA walker is composed of small amounts of dually-blocked walking strands and large amounts of dual-stem-loop track strands on gold nano -particles. The walking strand contains a swing arm domain and a DNAzyme domain blocked at both sides of catalytic core, while the track strand contains a substrate domain located at the peripheral larger loop. Only the presence of both ORF1ab and N RNA fragments can fully de-block the walking strand, which then continuously hybridizes with track strands and cleaves them by DNAzyme-catalyzed hydrolysis. As the cleavage of track strands from long-stranded, double stem-loop structure to short-stranded, linear sequence, the DNA walker shows much lowered stability due to decreased negative charge density and diminished steric repulsion, which then gets aggregated at high salt concentration, accompanied by a visible color change. The colorimetric DNA walker detects RNA fragments down to 1 nM, responds dual viral genes in a "AND" logic way, and shows high specificity to target sequence. It can further detect large nucleic acids containing ORF1ab and N sequences, and reach 200 copies/mL detection limit by coupling a simple upstream amplification of sample. The method may provide a convenient way for reliable detection of viral RNA.