Dual Signal Research Articles

Dual signal Amplification-Mediated Aptamer-Based electrochemical biosensor for sensitive detection of exosomes

Exosomes, a class of extracellular vesicles carrying the biological information of their parent cells, have emerged as one of the most promising biomarkers for the early screening and prognostic monitoring of cancer. However, the effective capture and sensitive detection of cancer cell-derived exosomes pose significant challenges due to the inevitable interference from internal environment and the limited exosome abundance in clinical samples. Herein, we proposed an aptamer-based electrochemical biosensor combining with Au nanoprobe-mediated dual signal amplification for sensitive detection of tumor-related exosomes. Benefiting from the specific recognition of CD63 aptamer (CD63 Apt), the target exosomes were efficiently captured on the gold electrode, followed by trapping the iDNA-modified Au nanoprobe, which could induce the generation of hybridization chain reaction (HCR). The long double-stranded DNA produced by HCR procedure provided numerous insertion sites to RuHex, achieving the high sensitivity for exosome detection. Under the optimal experimental conditions, this aptamer-based electrochemical biosensor for MCF-7 cancer cell-derived exosome detection exhibited a good linear range within 5 orders of magnitude (from 1.29 × 104 to 1.29 × 108 particle/mL) with a low limit of detection (LOD) to 1.65 × 103 particle/mL. Furthermore, this biosensor possessed good stability and anti-interference ability. Therefore, this analysis platform is considered as a promising candidate for the exosome-based diagnosis and prognosis of cancer in clinical applications.

Strand displacement amplification combining photothermal-colorimetric dual mode test strip for ultra-sensitive detection of patulin

Patulin (PAT) is a fungal toxin often found in fruit and juice products. The sensitive and fast detection of PAT can help the control of PAT-induced health risk. However, the lack of efficient and stable antibody for PAT hindered the advancement of its test strips. Here, we constructed a nucleic acid-based lateral flow test strip (NALFTS) and used photothermal-colorimetric dual mode for the detection of PAT. The binding of PAT in samples to the aptamer on magnetic separation probe MNPs-Apt@cDNA induced the release of cDNA competitively. Subsequently, cDNA initiates strand displacement amplification (SDA), generating numerous single-strand DNA (ssDNA). These ssDNA molecules were analyzed by a test strip with photothermal-colorimetric dual signal. The developed method demonstrated a limit of detection (LOD) of 5 pg mL−1 and a quantitative range of 0.01 ∼ 320 ng mL−1 in photothermal mode, and a LOD of 0.1 ng mL−1 and a quantitative range of 0.1 ∼ 40 ng mL−1 in colorimetric mode. This SDA-NALFTS offered dual signals corroborating each other to provide more reliable results for rapid screening or accurate monitoring of PAT in juice.

A ratiometric fluorescence platform based on bifunctional MOFs for sensitive detection of organophosphorus pesticides

Rapid and precise detection of organophosphorus pesticides (OPs) is of great importance for life health. Herein, a new sensing platform is developed through a dual signal amplification approach for sensitive quantification of OPs, with a bimetallic metal organic framework (UiO-66(Zr/Fe)-NH2) as peroxide-like nanozyme and fluorescent indicator. In the presence of thiocholine (TCh), the hydrolyzate of acetylthiocholine iodide catalyzed by acetylcholinesterase, the catalytic oxidization of o-phenylenediamine by UiO-66(Fe/Zr)-NH2 to strong fluorescent 2,3-diaminophenazine (λem 555nm) is significantly inhibited. OPs-triggered acetylcholinesterase inactivation enables the renaturation of UiO-66(Fe/Zr)-NH2. Interestingly, the introduction of 1,4-dioxane further boosts the amplification of fluorescence signals. By virtue of the recovered fluorescence at 555nm and MOF fluorescence (λem 446nm), the dual signal amplification-based ratiometric fluorescent platform is successfully employed for the selective recognition and sensitive detection of OPs. This work is expected to provide a facile and sensitive method for accurate OPs assay, and make a positive contribution to food safety.

An electrochemical biosensor for mercury(II) detection based on DNA-Au bio-bar codes coupled with enzymatic dual signal amplification

An electrochemical biosensor for mercury(II) detection based on DNA-Au bio-bar codes coupled with enzymatic dual signal amplification

Anchor carbon dots inside NH2-MIL-88B via ship-in-a-bottle strategy for dual signal enhancement in colorimetric-fluorescent sensors

The increase in oxytetracycline (OTC) pollution has become a significant risk to ecological stability and human health because of excessive use. Therefore, developing a precise and reliable sensor for trace OTC detection is critical. In this work, a dual-mode sensor of colorimetric-fluorescent (CL-FL) with dual signal-on was developed for OTC detection. Firstly, a novel carbon dots encapsulating in cavities of MOFs composite (CDs@NH2-MIL-88B) was constructed by the ship-in-a-bottle approach, which enhanced peroxidase-like activity and fluorescent intensity. Further, combining with surface molecularly imprinted polymer (MIP), the dual-mode sensor was constructed to develop selectivity (CDs@NH2-MIL-88B@rMIP). Finally, the dual signal enhancement mechanism of the sensor comes from the interaction between OTC and identifying binding site involving strong hydrogen bonding and metal complexation from imprinted cavity and CDs@NH2-MIL-88B, respectively. The prepared sensor has a linear detection range of 1.00 × 10-9 - 1.00 × 10-5M with the limit of detection (LOD) of 1.47 × 10-10M for the CL mode and a detection range of 1.00 × 10-11 -1.00 × 10-7M with the LOD of 1.84 × 10-12M for the FL mode. Meanwhile, the sensor shows high sensitivity, accuracy and reliability in OTC detection. Overall, this work provides a promising CL-FL dual-mode sensing systems with signal-on in the detection of antibiotics and other hazardous pollutants.

A River Water Quality Prediction Method Based on Dual Signal Decomposition and Deep Learning

Traditional single prediction models struggle to address the complexity and nonlinear changes in water quality forecasting. To address this challenge, this study proposed a coupled prediction model (RF-TVSV-SCL). The model includes Random Forest (RF) feature selection, dual signal decomposition (Time-Varying Filtered Empirical Mode Decomposition, TVF-EMD, and Sparrow Search Algorithm-Optimized Variational Mode Decomposition, SSA-VMD), and a deep learning predictive model (Sparrow Search Algorithm-Convolutional Neural Network-Long Short-Term Memory, SSA-CNN-LSTM). Firstly, the RF method was used for feature selection to extract important features relevant to water quality prediction. Then, TVF-EMD was employed for preliminary decomposition of the water quality data, followed by a secondary decomposition of complex Intrinsic Mode Function (IMF) components using SSA-VMD. Finally, the SSA-CNN-LSTM model was utilized to predict the processed data. This model was evaluated for predicting total phosphorus (TP), total nitrogen (TN), ammonia nitrogen (NH3-N), dissolved oxygen (DO), permanganate index (CODMn), conductivity (EC), and turbidity (TB), across 1, 3, 5, and 7-d forecast periods. The model performed exceptionally well in short-term predictions, particularly within the 1–3 d range. For 1-, 3-, 5-, and 7-d forecasts, R2 ranged from 0.93–0.96, 0.79–0.87, 0.63–0.72, and 0.56–0.64, respectively, significantly outperforming other comparison models. The RF-TVSV-SCL model demonstrates excellent predictive capability and generalization ability, providing robust technical support for water quality forecasting and pollution prevention.

Selenopolysaccharide Isolated from Lentinula edodes Mycelium Affects Human T-Cell Function.

Lentinula edodes polysaccharides are natural immunomodulators. SeLe30, analyzed in this study, is a new mixture of selenium-enriched linear 1,4-α-glucans and 1,3-β- and 1,6-β-glucans isolated from L. edodes mycelium. In the present study, we evaluated its immunomodulatory properties in human T cells. Peripheral blood mononuclear cells (PBMCs) and T cells were isolated from healthy donors' buffy coats. The effects of SeLe30 on CD25, CD366, and CD279 expression, the subsets of CD8+ T cells, and IFN-γ, IL-6, and TNF-α production were analyzed. SeLe30 downregulated CD25, CD279, and CD366 expression on T cells stimulated by the anti-CD3 antibody (Ab) and upregulated in unstimulated and anti-CD3/CD28-Abs-stimulated T cells. It increased the percentage of central memory CD8+ T cells in unstimulated PBMCs and naïve and central memory T cells in anti-CD3-Ab-stimulated PBMCs. SeLe30 decreased the number of central memory and naïve CD8+ T cells in anti-CD3/CD28-stimulated T cells, whereas, in PBMCs, it reduced the percentage of effector memory CD8+ T cells. Moreover, SeLe30 upregulated cytokine production. SeLe30 exhibits context-dependent effects on T cells. It acts on unstimulated T cells, affecting their activation while increasing the expression of immune checkpoints, which sensitizes them to inhibitory signals that can silence this activation. In the case of a lack of costimulation, SeLe30 exhibits an inhibitory effect, reducing T-cell activation. In cells stimulated by dual signals, its effect is further enhanced, again increasing the "safety brake" of CD366 and CD279. However, the final SeLe30 effect is mediated by its indirect impacts by altering interactions with other immune cells.

Simultaneous generation of dual 16-QAM-modulated millimeter-wave signals enabled by precoding-based optical I/Q modulation and single photodetector detection

Integration of quadrature-amplitude-modulation (QAM) modulation and millimeter-wave (mm-wave) technology ensures a concise enhancement of transmission capacity and peak data rates in radio-over-fiber (RoF) systems. Nevertheless, with the continuous development of new-generation mobile applications, higher demands on access flexibility have also been formulated. We propose a novel, to the best of our knowledge, dual 16-QAM-modulated mm-wave signal generation scheme for the simultaneous generation and transmission of two independent 16-QAM signals with different carrier frequencies, enhancing the channel capacity, spectrum efficiency, and access flexibility of the RoF systems. In our proposed scheme, the generation of the optical dual 16-QAM-modulated mm-wave signals is implemented by a precoding-based optical in-phase/quadrature (I/Q) modulator operating at optical carrier suppression (OCS) mode, and their detection is implemented by a single photodetector (PD). At the transmitter side, two independent driving QAM vector radio-frequency (RF) signals with precoding, generated via digital signal process (DSP), are fed into two parallel Mach–Zehnder modulators (MZMs) of an I/Q modulator to implement OCS modulation. The I/Q modulator generates optical carriers carrying both information from different QAM signals simultaneously. After square-law detection in a single PD, we generate the desired dual 16-QAM-modulated mm-wave signals with photonic frequency-doubling and recover the original 16-QAM signals without information distortion. Based on our proposed scheme, we experimentally demonstrate the simultaneous generation and transmission of 2-Gbaud dual 16-QAM-modulated mm-wave signals with carrier frequencies of 26 GHz and 40 GHz, respectively. After transmission over 10-km single-mode fiber (SMF) link and 1.2-m wireless link, the dual 16-QAM signals can be successfully separated and demodulated by a common DSP. Bit-error ratios (BERs) of both recovered 16-QAM signals can reach the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10−3. Compared with the existing schemes, our scheme only requires one-half of the driving frequency to generate dual 16-QAM-modulated mm-wave signals with the same carrier frequency. The result indicates that our proposed scheme can lower bandwidth requirements for optoelectronics devices, along with implementing better spectral efficiency and receiver sensitivity, which is more applicable to the demands for increased system capacity and multi-frequency access flexibility in future systems.

Construction of a Fluorescence/Phase-Change Dual-Mode Sensor Based on Carbon Dots/Poly(acrylic acid) for Highly Selective and Sensitive Detection of Ferric Ions.

Fe3+ is one of the crucial metal ions in biological systems, and its excess or deficiency in the body can trigger various diseases, posing a serious threat to human health. Moreover, improper handling or disposal of Fe3+ can lead to water pollution, thereby harming the environment. Therefore, the development of highly selective and sensitive Fe3+ detection probes is particularly urgent. In this paper, a dual-mode sensor based on sol-gel and fluorescence signal responses was developed for the visual detection of Fe3+. The visual sensing method based on the simultaneous response of Fe3+-triggered dual signals can minimize the interference from false-positive signals and enhance detection accuracy. The dual-mode sensor, denoted as PAA@CDs, was constructed by incorporating high-brightness (high fluorescence emission intensity) green-yellow carbon dots (CDs) into poly(acrylic acid) (PAA), which possesses a large number of carboxyl functional groups. Based on the interaction of Fe3+ with the surface functional groups of CDs, nonfluorescent complexes are formed, leading to nonradiative electron transfer, which induces fluorescence quenching and produces a fluorescence signal visible to the naked eye. Additionally, the interaction of Fe3+ with the carboxyl groups of PAA triggers the cross-linking of PAA, causing a sol-gel phase change signal. Consequently, the PAA@CDs exhibit a dual-response signal in Fe3+ detection. Based on the fluorescence method, the linear detection range of PAA@CDs for Fe3+ is 0.05-2.60 mM with a limit of detection (LOD) of 5.14 μM. Meanwhile, using the sol-gel method, the linear detection range is 0.02-2.20 mM, and the LOD is 42.5 μM. Furthermore, the PAA@CDs probes can be successfully applied to the detection of Fe3+ in real water samples, demonstrating their potential value in the analysis of real samples containing multiple ions.

A novel portable in situ analyzer for highly sensitive monitoring of organophosphorus and carbamate pesticides in food and environment

The presence of excessive residues of organophosphorus (OPs) and carbamate (CPs) pesticides in food and the environment poses a significant threat to human health and ecological sustainability. Herein, we reported a dual-readout, portable, and highly sensitive photoelectric analyzer (DPHP-analyzer) to achieve rapid and accurate monitoring of OPs and CPs. The dual signal strategy is mainly achieved by controlling the activity of acetylcholinesterase (AChE) in the presence of OPs to catalyze acetylthiocholine (ATCh) and generate thiocholine (TCh), which specifically induced the conversion of colorless Ellman's reagent (DTNB) into yellow 5-thio-2-nitrobenzoic acid (TNB). Simultaneously, the utilization of positively charged TNB as an absorber can induce a dynamic fluorescence quenching effect based on energy transfer mechanism. Fully cooperating with the above mechanism, a CD like, disposable array-based chip manufactured by 3D printing (CD-AN-chip) was designed and integrated to deliver reagents. By use of this dual-output strategy, the analyzer and chip can provide good sensitivity and selectivity for the monitoring of diazinon and carbendazim (case analysis) with a LOD 0.38 ng/mL for carbendazim. And the reproducibility, stability and practicability analysis of real sample have been thoroughly validated simultaneously. Importantly, with the features of fluorescence fingerprint map, the detector could be employed for the distinction of various analytes and further be used for monitoring the nutritional environment within residential and public settings.

Gold Nanoparticles-Based Colorimetric Immunoassay of Carcinoembryonic Antigen with Metal–Organic Framework to Load Quinones for Catalytic Oxidation of Cysteine

This work reported gold nanoparticles (AuNPs)-based colorimetric immunoassay with the Cu-based metal–organic framework (MOF) to load pyrroloquinoline quinone (PQQ) for the catalytic oxidation of cysteine. In this method, both Cu2+ and PQQ in the MOF could promote the oxidation of inducer cysteine by redox cycling, thus limiting the cysteine-induced aggregation of AuNPs and achieving dual signal amplification. Specifically, the recombinant carcinoembryonic antigen (CEA) targets were anchored on the MOF through the metal coordination interactions between the hexahistidine (His6) tag in CEA and the unsaturated Cu2+ sites in MOF. The CEA/PQQ-loaded MOF could be captured by the antibody-coated ELISA plate to catalyze the oxidation of cysteine. However, once the target CEA in the samples bound to the antibody immobilized on the plate surface, the attachment of CEA/PQQ-loaded MOF would be limited. Cysteine remaining in the solution would trigger the aggregation of AuNPs and cause a color change from red to blue. The target concentration was positively related to the aggregation and color change of AuNPs. The signal-on competitive plasmonic immunoassay exhibited a low detection limit with a linear range of 0.01–1 ng/mL. Note that most of the proteins in commercial ELISA kits are recombinant with a His6 tag in the N- or C-terminal, so the work could provide a sensitive plasmonic platform for the detection of biomarkers.

Microfluidic-SERS sensing system based on dual signal amplification and aptamer for gastric cancer detection.

Studies have found that matrix metalloproteinase-9 (MMP-9) and interleukin-6 (IL-6) play an important role in tumorigenesis. In order to detect MMP-9 and IL-6 concentrations with high sensitivity and specificity, an efficient microfluidic-SERS sensing system was prepared based on surface-enhanced Raman scattering (SERS). The aptamer recognition-release mechanism and the dual signal amplification strategy were applied in the sensing system. The sensor system was developed using two kinds of nanomaterials with excellent SERS properties, namely gold-coated iron tetroxide particles (Fe3O4@AuNPs) and gold nanocages (AuNCs). In addition, Fe3O4@AuNPs also has magnetic adsorption properties. In the sensing system, single-stranded DNA1 (ssDNA1) and aptamer were modified on Fe3O4@AuNPs. Single-stranded DNA2 (ssDNA2) and Raman tags were modified on AuNCs. When the target was present, the aptamer bound to the target and detached from the Fe3O4@AuNPs, andssDNA2 bound to the exposed ssDNA1. At this time, the Fe3O4@AuNPs@AuNCs@SERS tag complex was formed, and the SERS signal was enhanced for the first time. Under the action of an external magnet on the microfluidic chip, the complex was magnetized and enriched. The SERS signal was enhanced for the second time. Due to the high affinity between the aptamer and the target object, the sensing system has a strong specificity. The double amplification of the SERS signal gave the system excellent sensitivity. The limit of detection (LOD) relative to MMP-9 and IL-6 were as low as 0.178pg/mL and 0.165pg/mL, respectively. The microfluidic-SERS sensing system has a feasible prospect in the early screening of gastric cancer.

Dual signal amplification strategy-based electrochemical aptasensor utilizing redox molecule/MOF composites for multi-pesticide detection

Electrochemical aptasensor is a great tool for simultaneously assessing harmful pesticide residues in agricultural products and foods. This study ingeniously designed an electrochemical aptasensor based on dual signal amplification strategies for concurrent detection of various pesticide residues. Firstly, poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide (PR) and Au-Pt-Pd trimetallic nanoflowers supported on HP-UiO66-NH2 were creatively employed together as substrates to load more aptamers, ascribed to the improved conductivity, abundant sites and a large electrochemical effective surface area. Secondly, ferrocene-cysteine gold nanoparticles supported on CeMOF(Ⅲ, Ⅳ) and methylene blue-loaded MOF235 were innovatively engineered to build two distinctive signal labels, which displayed comparable large and stable signal currents among other redox molecule/MOF composites. Additionally, PR contributed further signal amplification. Consequently, the constructed aptasensor showed superior performance for simultaneous detection of acetamiprid (AD) and malathion (ML), with linear ranges from 10 pM to 0.1 μM and detection limits of 4.8 pM for AD and 0.51 pM for ML. Moreover, the aptasensor performed well in the assay of AD and ML in Chinese cabbage samples with high accuracy compared with a high-performance liquid chromatography-tandem mass spectrometry method. Overall, the strategies proposed herein provided a useful and potential route for general development of electrochemical aptasensors to simultaneously detect multiple pesticide residues.

Highly sensitive detection of DNA methyltransferase1 triggered by methylation protection

Type 2 diabetes is on the rise year by year, and 80 % of patients with type 2 diabetes die from cardiovascular complications. Strict control of blood glucose can significantly reduce the occurrence and development of diabetic microvascular complications, but can not effectively prevent the occurrence of diabetic macrovascular lesions. DNA methyltransferase 1 (DNMT1) plays an important role in developing phenotypic switching and secretion of inflammatory factors in vascular smooth muscle cells(VSMC), leading to the deregulation of vascular function. In this work, a biosensor based on methylation protection was designed. In the presence of the target DNMT 1, the formed methylation sites protect the dsDNA from being digested by the HpaII restriction enzyme. At the same time, a large number of G-quadruplex are produced by the catalyzed hairpin assembly (CHA) reaction cycle, and the peroxidase-like activity of G-tetraplex and hemin is used to continuously catalyze the color change of substrate ABTS, thus realizing dual signal amplification. The binding of magnetic beads to dsDNA effectively reduces the background signal and enables a highly selective and sensitive analysis of the target DNMT 1 in complex biological samples, with a detection limit as low as 0.22 UmL−1, showing a good linear relationship in the range of 0.22–10 UmL−1. A new approach for the study of macrovascular damage is provided in type 2 diabetes.

Design of a portable bioassay system based on highly efficent nanozyme and Au-DNA nanocluster: Toward current/colorimetric dual-signal detection of sugarcane smut

Sugarcane smut is a major agricultural pest affecting sugarcane yield and quality, posing a significant threat to the sustainable and healthy development of the global sugar industry. The best strategy for controlling Sugarcane smut is early and precise diagnosis. An intelligent mobile bio-platform is constructed based on Au-Co/Zn ZIF nanozymes and Au-DNA nanoclusters for current/colorimetric dual signal detection of the sugarcane smut pathogen. Efficient and specific cycling of the specific gene fragment (bE4′) for Sugarcane smut is achieved by strand displacement reaction. The output strand then forms Au-DNA nanoclusters with AuNPs-DNA, and the bioconjugate is captured by H2 probe, which results in the formation of more double-stranded structures, causing methylene blue (MB) to adsorb on electrode. The anodic nanozyme efficiently catalyzes the oxidation of glucose, generating a large number of electrons, and MB in the system is therefore reduced to MBH, causing a color change. This results in distinct current/colorimetric dual output signals, significantly enhancing the accuracy. A capacitor is further coupled with the system to improve the sensitivity. The detection signals are read in real-time by a smartphone. The developed method for sugarcane smut genes shows good linearity within a concentration range of 0.0001–10000 pM, with a detection limit as low as 23.59 aM (S/N = 3). This work integrates advanced technologies from various fields to create a portable sensing device with extremely high sensitivity and precision for detecting sugarcane smut. It provides a reliable new option for early and precise diagnosis of the disease and offers valuable theoretical and technical insights for early prevention, intelligent detection, and real-time monitoring of other plant diseases.

Highly sensitive β-amyloid1–42 oligomer aptamer-based assay via dual cyclic amplifications of three-way catalytic hairpin assembly and palindrome polymerase reaction

β-amyloid1–42 oligomer (AβO1–42), a neurotoxic protein, is considered the key factor in the progression of Alzheimer's disease (AD). And, high sensitivity detection of AβO1–42 is of considerable importance for the early diagnosis and deterioration prevention of AD. We present here an ultrasensitive fluorescent AβO1–42 detection approach based on aptamer recognition probes and a new dual cyclic signal amplification strategy by combining three-way catalytic hairpin assembly (3W-CHA) with palindromic sequence-based polymerase amplification (PBPA). Once the aptamers bind to target AβO1–42 molecules, ssDNA sequences are released to initiate 3W-CHA between three hairpins to unfold the signal hairpins and to form Y-shaped DNA structures (Y-DNAs). Subsequently, the assistance ssDNAs bind the Y-DNAs to expose the palindromic sequences to yield Y-DNA dimers, which lead to cyclic PBPA reaction with presence of polymerase to further unfold more signal hairpins for yielding considerably magnified fluorescence recovery, enabling sensitive assay of AβO1–42 down to 2.4 pM within a dynamic range of 5 pM∼50 nM. Furthermore, this strategy has been validated for interrogation of low AβO1–42 levels in artificial cerebrospinal fluid (CSF), suggesting its promising potential for application in early diagnosis and prevention of AD.

A dual-color ratiometric fluorescence sensor of biogenic amines with dye encapsulated covalent organic framework for meat freshness

Developing sensitive, nondestructive and real-time methods for assessing meat freshness is vital for ensuring food safety. Traditional monochromatic fluorescent probes for monitoring meat freshness markers like biogenic amines often face challenges in sensitivity, interference, visualization and portability for practical applications. Herein, we constructed a new Ru-Flu@COF fluorescence sensor, by combining a green fluorescent dye-encapsulated covalent organic framework (Flu@COF) with a red fluorescent compound (Ru(bpy)32+), exhibiting a dual inverse ratiometric fluorescence signal towards essential biogenic amines His and NH3·H2O, thus achieving a rich color gradient and spoilage-sensitive color discrimination. The detection linear range for His and NH3·H2O was 0.6∼200 μM and 0.5∼60 mg/L, with limits of detection of 0.5 μM and 0.2 mg/L, respectively. Furthermore, Ru-Flu@COF gel labels together with a smartphone enable portable, in situ and naked-eye monitoring freshness of pork, fish and shrimp, where the freshness level can be visually identified through the gel label color from red (fresh) to orange (less fresh), yellow (spoilage) and green (severe spoilage). The proposed smart label has the advantages of high sensitivity, excellent visual discrimination and portability, and it can be a promising platform for in situ nondestructive monitoring freshness of various kinds of meat for food safety inspection in the future.

Fe7S8 nanosheets- catalyzed colorimetric and fluorescence dual ratio sensing for high selectivity detection of ascorbic acid

By using Fe7S8 nanosheets (NSs) as catalyst, O-phenylenediamine (OPD) as chromogenic substrate, H2O2 as oxidant, and ascorbic acid (AA) as regulator, a dual ratio colorimetric and fluorescence sensing system for determining AA was constructed. The inherent peroxidase like activity of Fe7S8 NSs enables it to catalyze the oxidation of OPD in the existence of H2O2, resulting in the formation of yellow-colored 2, 3-diaminophenazine (DAP) with a characteristic absorption peak at 450 nm and a fluorescence emission peak at 560 nm. However, the presence of AA could suppress the oxidation of OPD and induce the generation of quinoxaline derivative (QXD) 3-(dihydroxyethyl) furo [3,4-b] quinoxaline-1-one with absorption and fluorescence emission peaks located at 345 and 435 nm, respectively. Thus, employing the absorption of QXD at 345 nm and emission at 435 nm as the reporting signals, and the absorption of DAP at 450 nm and emission at 560 nm as the reference signals, a ratio colorimetric (A345/A450) and ratio fluorescence (F435/F560) dual signal detection method for AA was developed. Under the optimized conditions, the value of A345/A450 was found to be linear with AA concentration in the ranges of 1.0–40 μM and 40–100 μM, and the value of F435/F560 was strongly correlated with AA concentration in the ranges of 1.0–30 μM and 30–100 μM. When applied for the assay of AA in human serum samples, an acceptable recovery ranging from 93.1 to 106.6 % was obtained, confirming the potential of the sensing system in practical applications.

Electrochemical synthesis of multicolor carbon dots with room temperature phosphorescence to thermally activated delayed fluorescence via surface state modulation

Solid-state multicolor carbon dots (CDs) have attracted tremendous attention due to their wide applications. However, the fluorescence quenching of solid-state CDs occurs due to the π-π stacking or energy transfer between adjacent carbon dots. In addition, it is difficult to observe the afterglow of solid-state CDs due to their self-quenching and deliquescence. Here, electrochemically prepared multicolor CDs emit the solid-state fluorescence and afterglow emission with lifetimes up to 657 ms by embedding the CDs into urea matrix. More importantly, the surface amino groups and C = O bonds regulate the afterglow emission of CDs from phosphorescence and thermally activated delayed fluorescence at room temperature. Surface amino groups of multicolor CDs can enhance the spin–orbit coupling, increase the intersystem crossing (ISC) and reverse intersystem crossing (RISC). Thus it can promote the generation of triple excited states and regulate the singlet–triplet energy gap value from 0.384 to 0.026 eV. The formation of covalent bonds stabilizes the single and triple excited states and inhibits the non-radiative recombination, which achieves the enhanced fluorescence and visual afterglow of multicolor CDs. The fluorescence and afterglow CDs can be applied to dual signal imaging and anti-counterfeiting, which broadens the practical applications for solid-state CDs via surface state modulation.

Triple-Branch Catalytic Assembly DNAzyme Motivated DNA Tweezer for Sensitive and Reliable mecA Gene Detection in Staphylococcus aureus.

Staphylococcus aureus (S. aureus, SA) is one of the most common bacteria in nosocomial infections. Sensitive and efficient analysis of methicillin-resistance of SA is crucial for improving the nursing performance of pneumonia. However, methicillin-resistance analysis with favorable sensitivity and specificity in an enzyme-free manner remains a huge challenge. This paper presents the development of a new fluorescent biosensor for detecting mecA gene using a triple-branch catalytic hairpin assembly (CHA) triggered DNAzyme switch-based DNA tweezer. The SA from the samples are immobilized on the plate's surface using the protein A antibody. The biosensor possesses several key features. Firstly, it utilizes dual signal amplification processes, specifically the triple-branch CHA and DNAzyme controlled DNA tweezer-based signal recycling, to enable mecA detection on the plate. This design enhances the method's sensitivity, resulting in a low limit of detection of 1.5 fM. Secondly, the biosensor does not rely on enzymes for mecA analysis, ensuring a high level of stability during target analysis. Lastly, the method demonstrates a remarkable selectivity by accurately distinguishing target sequences from non-target sequences. The proposed biosensor, which does not require enzymes and has a high level of sensitivity, offers a viable platform for the rapid and simple quantification of mecA in SA.