Dual Signal Research Articles

DNAzyme-driven tripedal DNA walker for ratiometric electrochemical aptasensor ultrasensitive detection of aflatoxin B1

Aflatoxin B1 is a potent carcinogen widely found in agricultural products and feed. Therefore, investigating the development of convenient, sensitive, and precise techniques for detecting AFB1 is critical. This work proposes a ratiometric electrochemical aptasensor based on DNAzyme-driven tripedal DNA walker for enzyme-free AFB1 detection. The design of multiple legs reduces the moving time on the electrode surface and enhances the value of signal response. In this approach, the tagging of ferrocene and methylene blue as signal switch molecules diminishes the impact of interferences and significantly enhances the reproducibility (RSD: 2.825%). Meanwhile, the tripedal DNA walker and DNAzyme dual signal amplification enabled the sensor to detect AFB1 traces in cereals. We achieved trace detection of AFB1 with a detection limit of 61 fg/mL and a wide linear range from 0.0001 to 10 ng/mL. Furthermore, the aptasensor success rate was comparable to that of HPLC-PMP. The results demonstrate enormous potential for detection. Furthermore, the method can detect various targets by altering the target aptamer, displaying attractive scalability. This suggests its tremendous prospective in detecting mycotoxins in food in the future.

Sensitive small extracellular vesicles associated circRNAs analysis combined with machine learning for precision identification of gastric cancer

Small extracellular vesicle associated circular RNAs (sEV-circRNAs) are emerging as promising biomarkers for gastric cancer diagnosis. Current research predominantly focuses on identifying these biomarkers through high-throughput sequencing. However, there has been insufficient exploration into the practical application of sEV-circRNAs for early gastric cancer diagnosis. In this study, we developed a sensitive electrochemical platform that leverages tetrahedron-Dox-AuNPs (TDA) tag and DNA tetrahedron-enhanced catalytic hairpin assembly (DT-CHA) to detect sEV-circRNAs. Based on the dual signal amplification of the TDA tag and DT-CHA, the platform can achieve low-concentration detection of the target, with a detection limit of 153.1 aM and a linear range from 1 fM to 1 nM. By profiling four sEV-circRNAs (circNRIP1, circRANGAP1, circCORO1C, and circSHKBP1) in a gastric cancer cohort and combining suitable ML diagnostic model, this platform performed well in distinguishing healthy donors from early GC patients. Thus, this confluence of a multi-biomarker approach with machine learning analysis, applied to plasma sEV-circRNAs, emerges as an important strategy for cancer screening.

Ultrasensitive Ti3C2Tx@Pt-Based Immunochromatography with Catalytic Amplification and a Dual Signal for the Detection of Chloramphenicol in Animal-Derived Foods.

Herein, a catalytic amplification enhanced dual-signal immunochromatographic assay (ICA) based on Pt nanoparticles (Pt NPs) modified with Ti3C2Tx MXene (Ti3C2Tx@Pt) was first developed for chloramphenicol (CAP) in animal-derived foods. Due to the large specific surface area and abundant active sites of Ti3C2Tx@Pt, they can be loaded with hundreds of Pt NPs to enhance their catalytic activity, resulting in a significant increase in the detection sensitivity; the sensitivity was up to 50-fold more sensitive than the reported ICA for CAP. The LODs of the developed method for milk/chicken/fish were 0.01 μg/kg, the LOQs were 0.03 μg/kg and the recovery rates were 80.5-117.0%, 87.2-118.1% and 92.7-117.9%, with corresponding variations ranging from 3.1 to 9.6%, 6.0 to 12.7% and 6.0 to 13.6%, respectively. The linear range was 0.0125-1.0 μg/kg. The results of the LC-MS/MS confirmation test on 30 real samples had a good correlation with that of our established method (R2 > 0.98), indicating the practical reliability of the established method. The above results indicated that an ICA based on the Ti3C2Tx@Pt nanozyme has excellent potential as a food safety detection tool.

Dual wavelength signal generation with four wave mixing based on directly modulated laser

Dual wavelength (DW) lasers are crucial for producing petahertz (PHz) signals, which are higher value terahertz (THz) signals. The infrared and visible light sub-bands are valuable frequency range for a number of applications, including networking, multiple access techniques, next-generation mobile networks (6G), future wireless networks, and new PHz communication systems. The importune need to the high frequency signal such as THz and PHz signal for 5 and 6 next generation wireless cellular mobile networks motivate us to design an optical system to provide these signals rather than an electronic circuits. They are also beneficial for a variety of medical testing. The wavelength spacing ranging from 14 nm to 7 nm is proposed and demonstrated a dual-wavelength generation with FWM based on DML is realized at 1554 and 1548 nm. It is essential to make use of the fiber's non-linearity characteristics to ensure synchronization for continuous wave (CW) laser and directly modulated laser (DML) signals and the creation of the four wave mixing (FWM) components. With the help of OptiSystem version 14.0, the system is designed and investigated then, the desired THz signal is created as pulse amplitude modulation. The position of the FWM components within the frequency range between the spectrums of the two lasers affects the synthesis of the required signal. At the DML frequency equal to or below the CW Laser (1520 nm), neither FWM frequency components nor dual wavelength pulses exist. On the other hand, the FWM frequency components and dual wavelength pulses can only be seen when the DML frequency is greater than 1520 nm. The CW laser frequency is the main controlling factor in the generation THz signal. If the CW laser frequency is set at or below 1520 nm, the dual wavelength and THz signal are accessible. Because these frequencies are so far from the reference fiber frequency, it is impossible to produce dual wavelength pulses at frequencies higher than those mentioned above.

Dual threshold input receiver FPGA-only signal digitization method for time-of-flight positron emission tomography

As silicon photomultiplier (SiPM)-based time-of-flight (TOF) positron emission tomography (PET) becomes popular, the need for sophisticated PET data acquisition (DAQ) systems is increasing. One promising solution to this challenge is the adoption of a field-programmable gate array (FPGA)-only signal digitization method. In this paper, we propose a new approach to efficiently implement an FPGA-only digitizer. We configured the input/output (IO) port of the FPGA to function as a dual-threshold voltage comparator through the use of simple passive circuitry and heterogeneous IO standards. This configuration overcomes the limitations of existing methods by allowing different threshold voltages for adjacent IO pins, effectively reducing routing complexity and lowering manufacturing costs. An FPGA-only digitizer was implemented by integrating the dual-threshold voltage comparator and FPGA-based time-to-digital converter. By combining the dual-threshold time-over-threshold (TOT) method and curve fitting, precise energy information could be obtained. The performance of the FPGA-only digitizer was assessed using a detector setup comprising a 3 × 3 × 20 mm3 LYSO scintillation crystal and a single pixel SiPM. Using the configured evaluation setup, an energy resolution of 12.5% and a time resolution of 146 ± 9 ps were achieved for a 20 mm scintillation crystal. The dual-threshold TOT implemented using the proposed method showed consistent linearity across an energy range of 100 keV to 600 keV. The proposed method is well-suited for the development of cost-effective DAQ systems in highly integrated TOF PET systems.

Fluorescein@NH2-UiO-66 Probe for Ratiometric Fluorescence Sensing of Trace Phosphate in Water

Phosphate pollution leads to deterioration in water quality, posing a serious threat to human health. Therefore, it is important to develop a highly selective and sensitive fluorescent probe for phosphate detection. Here, we report a novel ratiometric fluorescent probe, Fluorescein@NH2-UiO-66 (denoted as Flu@NH2-UiO-66), for the trace detection of phosphate in water. Specifically, during the in situ solvothermal synthesis of Flu@NH2-UiO-66, fluorescein molecules were encapsulated into the cavities of the metal-organic framework. Furthermore, the encapsulation amount of fluorescein was controlled by adjusting the acidity of the system. The Flu@NH2-UiO-66 (60 H+) sample, prepared with a 60:1 molar ratio of acetic acid to the metal center exhibited distinct dual fluorescence signal peaks. The probe showed a highly selective fluorescence response to phosphate. Within a range of 0–20 μM phosphate concentration, the probe demonstrated excellent linear detection capability with a detection limit of 0.37 μM. Moreover, the mechanism of fluorescence enhancement can be attributed to the addition of phosphate, which greatly increases the UV absorbance of the probe. This study developed a novel ratiometric fluorescent probe capable of rapid, sensitive, and stable detection of trace phosphate, which is of great significance for environmental management.

Fe-single-atom catalysts boosting electrochemiluminescence via bipolar electrode integrated with its peroxidase-like activity for bioanalysis

Multifunctional single-atom catalysts (SACs) have been extensively investigated as outstanding signal amplifiers in bioanalysis field. Herein, a type of Fe single-atom catalysts with Fe-nitrogen coordination sites in nitrogen-doped carbon (Fe–N/C SACs) was synthesized and demonstrated to possess both catalase and peroxidase-like activity. Utilizing Fe–N/C SACs as dual signal amplifier, an efficient bipolar electrode (BPE)-based electrochemiluminescence (ECL) immunoassay was presented for determination of prostate-specific antigen (PSA). The cathode pole of the BPE-ECL platform modified with Fe–N/C SACs is served as the sensing side and luminol at the anode as signal output side. Fe–N/C SACs could catalyze decomposition of H2O2 via their high catalase-like activity and then increase the Faraday current, which can boost the ECL of luminol due to the electroneutrality in a closed BPE system. Meanwhile, in the presence of the target, glucose oxidase (GOx)-Au NPs-Ab2 was introduced through specific immunoreaction, which catalyzes the formation of H2O2. Subsequently, Fe–N/C SACs with peroxidase-like activity catalyze the reaction of H2O2 and 4-chloro-1-naphthol (4-CN) to generate insoluble precipitates, which hinders electron transfer and then inhibits the ECL at the anode. Thus, dual signal amplification of Fe–N/C SACs was achieved by increasing the initial ECL and inhibiting the ECL in the presence of target. The assay exhibits sensitive detection of PSA linearly from 1.0 pg/mL to 100 ng/mL with a detection limit of 0.62 pg/mL. The work demonstrated a new ECL enhancement strategy of SACs via BPE system and expands the application of SACs in bioanalysis field.

Dual-channel sensing strategy for melatonin detection based on iron-cobalt oxide nanosheets with peroxidase-like activity and gold nanoclusters

This work developed a sensitive fluorescence and colorimetric dual-channel sensing system for melatonin determination based on iron-cobalt oxide nanosheets (FeCo-ONSs) and gold nanoclusters (AuNCs). FeCo-ONSs exhibited excellent peroxidase (POD)-like activities, that could catalyze H2O2 to produce reactive oxygen species and further catalyze N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium (TOPS) to couple with 4-amino-antipyrine (4-AAP) to generate purple compounds (PCs), which had absorption at 549 nm. The generated PCs can quench the fluorescence of AuNCs at 577 nm via fluorescence resonance energy transfer (FRET). The process of the generation of purple compounds would be restrained in existence of melatonin due to its scavenging capacity for free radicals. As a consequence, the absorption at 549 nm decreased, while the fluorescence quenching of AuNCs was weakened, and emission intensity at 577 nm progressively recovered. The recovery of fluorescence and the decrease in absorption depended on the concentration of melatonin. Therefore, by employing fluorescence and colorimetric dual signal monitoring, the linear ranges of melatonin were 5–300 μM and 5–800 μM, and the LODs were 1.17 μM and 2.13 μM, respectively.

A novel electrochemical aptamer biosensor for lead (Ⅱ) ion detection utilizing GO/PAMAM @Au and Au/MB as dual signal amplifiers

A competitive electrochemical aptamer biosensor for the selective detection of Pb2+ was developed in this study. The PAMAM@Au hybrid materials and the bioprobe MB-GNPs-ssDNA were synthesized with chemical methods. Modified electrode with carboxylated graphene oxide was prepared via electrodeposition. PAMAM@Au was immobilized on the modified electrode using the EDC/NHS crosslinker, and aptamer (Apt) was bound to PAMAM@Au hybrid materials using the glutaraldehyde crosslinker. The assembly of MB-GNPs-ssDNA/Apt/PAMAM@Au/GO/SPCE biosensors was achieved through immobilizing bioprobe onto electrodes, based on the theory of aptamer-complementary chain reactions. The fabricated biosensor was characterized through electrochemical experiments, SEM, AFM, TEM, XPS and FTIR. The biosensor's performance was evaluated in a series of Pb2+ aqueous solutions by differential pulse voltammetry (DPV), and the results demonstrated this biosensor had excellent repeatability, stability, and specificity. The detection range spanned from 0.5 pM/L to 500 nM/L, with a detection limit of 5 fM/L. Consequently, the proposed biosensor can serve as a reliable analytical tool for the sensitive detection of lead ions.

DCCS: A dual congestion control signals based TCP for datacenter networks

As cloud computing advances, datacenter networks (DCNs) face unprecedented pressure due to the increasing prevalence of high bandwidth and low delay applications. Current reliable transmission protocols such as TCP harness packet loss, network delay, and Explicit Congestion Notification (ECN) for congestion control, aiming to maintain low latency and high throughput. We investigate the efficacy of ECN-based protocols against incast congestion in one-hop networks and delay-based protocols for maintaining low end-to-end delay in multi-hop networks, at the expense of throughput fairness. Thus, we introduce a novel TCP protocol, Dual Congestion Control Signals (DCCS), merging ECN and delay signals for a broader congestion control mechanism. DCCS effectively handles burst traffic, prevents packet loss, ensures low end-to-end delay, and resolves throughput unfairness by determining a precise minimum round-trip time (RTT) for each flow through a drain signal. Simulations on ns-3 confirm that DCCS surpasses ECN-based (i.e., DCTCP), delay-based (i.e., DC-Vegas and Swift), and hybrid-based protocols (i.e., EAR) in fat-tree topology under realistic workload, cutting down Flow Completion Time (FCT) by 3.8%–20.5%. This substantiates DCCS’s competency in providing high-quality service for DCNs.

Programmable Entropy-Driven Circuit-Cascaded Self-Feedback DNAzyme Network for Ultra-Sensitive Fluorescence and Photoelectrochemical Dual-Mode Biosensing.

Inspired by natural DNA networks, programmable artificial DNA networks have become an attractive tool for developing high-performance biosensors. However, there is still a lot of room for expansion in terms of sensitivity, atom economy, and result self-validation for current microRNA sensors. In this protocol, miRNA-122 as a target model, an ultrasensitive fluorescence (FL) and photoelectrochemical (PEC) dual-mode biosensing platform is developed using a programmable entropy-driven circuit (EDC) cascaded self-feedback DNAzyme network. The well-designed EDC realizes full utilization of the DNA strands and improves the atomic economy of the signal amplification system. The unique and rational design of the double-CdSe quantum-dot-released EDC substrate and the cascaded self-feedback DNAzyme amplification network significantly avoids high background signals and enhances sensitivity and specificity. Also, the enzyme-free, programmable EDC cascaded DNAzyme network effectively avoids the risk of signal leakage and enhances the accuracy of the sensor. Moreover, the introduction of superparamagnetic Fe3O4@SiO2-cDNA accelerates the rapid extraction of E2-CdSe QDs and E3-CdSe QDs, which greatly improves the timeliness of sensor signal reading. In addition to the strengths of linear range (6 orders of magnitude) and stability, the biosensor design with dual signal reading makes the test results self-confirming.

A ratiometric electrochemical biosensor based on ARGET ATRP for detection of HER2 gene

Human epidermal growth factor receptor 2 (HER2), a common proto-oncogene, is overexpressed in a subset of breast cancer patients. It is essential to track HER2 expression for early breast cancer diagnosis. Herein, a ratiometric electrochemical biosensor for detection of HER2 based on activators generated by electron transfer for atom transfer radical polymerisation (AGET ATRP) and hairpin DNA was developed. Specifically, hairpin DNA was first self-assembled on the gold electrode by Au–S bond. Upon capturing HER2, the stem-loop structure of hairpin DNA was unfolded, the signal value of methylene blue (MB) decreased as it moved away from the electrode surface. cDNA was linked with HER2 by complementary base pairing to introduce amino group. Then, the initiator 2-bromo-2-methylpropionic acid (BMP) were connected to the amino group on the cDNA to activate ARGET ATRP. The detection performance of biosensors for HER2 was explored by the ratio signal between two signal molecules. Under optimal conditions, this ratiometric electrochemical biosensor shows good selectivity and stability with a wide detection range of 1–1 × 106 pM and a detection limit of 78.47 fM. Furthermore, the biosensor exhibits satisfactory anti-interference ability due to the hairpin DNA and dual signal system, and has promising application prospects in the detection of other DNA disease markers.

Enhanced electrochemical detection of thrombin via a dual signal amplification strategy based on Au Nanoparticles@Carbon nanosheets and PtCu3 nanoparticles

Thrombin (TB) is an enzyme involved in blood coagulation and associated with various diseases such as thromboembolic disease, Alzheimer's disease, and cancer. This study introduces an electrochemical biosensor with a sandwich-type structure designed for the highly sensitive detection of TB. The working electrode (WE) was modified with gold nanoparticles loaded onto the carbonization product of two-dimensional Cu-bond tetrakis(4-carboxyphenyl)porphyrin (Cu-TCPP) nanosheets (referred to as Au@CNSs), enhancing the electrical conductivity and specific surface area of the WE. The modified electrode exhibited notable catalytic activity for H2O2 reduction. One aptamer of TB (Apt1), with a sulfhydryl group (-SH-) at the end, can tightly bound to Au@CNSs through a S-Au bond. Additionally, PtCu3 alloy nanocrystals, possessing high electrocatalytic activity towards H2O2 reduction, were prepared and modified with another TB aptamer (Apt2). In the presence of TB, a sandwich-type biosensing interface formed, resulting in an increased reduction current for H2O2. Under optimized conditions, the proposed aptasensor demonstrated a broad linear range from 0.01 pM to 32 nM and a low detection limit of 0.005 pM. Furthermore, the aptasensor exhibited excellent performance in terms of stability, reproducibility, and sensitivity, making it a promising tool for TB detection in human serum.

Dual Engine Boosts Organic Photoelectrochemical Transistor for Enhanced Modulation and Bioanalysis.

Organic photoelectrochemical transistor (OPECT) has shown substantial potential in the development of next-generation bioanalysis yet is limited by the either-or situation between the photoelectrode types and the channel types. Inspired by the dual-photoelectrode systems, we propose a new architecture of dual-engine OPECT for enhanced signal modulation and its biosensing application. Exemplified by incorporating the CdS/Bi2S3 photoanode and Cu2O photocathode within the gate-source circuit of Ag/AgCl-gated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) channel, the device shows enhanced modulation capability and larger transconductance (gm) against the single-photoelectrode ones. Moreover, the light irritation upon the device effectively shifts the peak value of gm to zero gate voltage without degradation and generates larger current steps that are advantageous for the sensitive bioanalysis. Based on the as-developed dual-photoelectrode OPECT, target-mediated recycling and etching reactions are designed upon the CdS/Bi2S3, which could result in dual signal amplification and realize the sensitive microRNA-155 biodetection with a linear range from 1 fM to 100 pM and a lower detection limit of 0.12 fM.

DNA-functionalized MOF fluorescent probes for the enzyme-free and pretreatment-free detection of MicroRNA in serum

MicroRNA (miRNA) is a promising biomarker that plays an important role in various biomedical applications, especially in cancer diagnosis. However, the current miRNA detection technology has inherent limitations such as complex operation, expensive testing cost and excessive detection time. In this study, a dual signal amplification biosensor based on DNA-functionalized metal–organic frameworks (MOFs) fluorescent probes, MFPBiosensor, was established for the enzyme-free and pretreatment-free detection of the colon cancer (CC) marker miR-23a. DNA-functionalized MOFs NH2-MIL-53(Al) (DNA@MOFs) were synthesized as fluorescent probes with specific recognition functions. A single DNA@MOF carries a large number of fluorescent ligands 2-aminoterephthalic acid (NH2–H2BDC), which can generate strong fluorescence signals after alkaline hydrolysis. Combined with catalyzed hairpin assembly (CHA), an efficient isothermal amplification technique, the dual signal enhancement strategy reduced matrix interference and sensitized the signal response. The established MFPBiosensor successfully detected extremely low levels of miRNA in complex biological samples with acceptable sensitivity and specificity. With a single detection cost of $0.583 and a test time of 50 min, the excellent inexpensive and rapid advantage of the MFPBiosensor is highlighted. More importantly, the subtle design enables the MFPBiosensor to achieve convenient batch detection, where miRNA in serum can be directly detected without any pretreatment process or enzyme. In conclusion, MFPBiosensor is a promising biosensor with substantial potential for commercial miRNA detection and clinical diagnostic applications of CC.

Metal-Graphene Hybrid Terahertz Metasurfaces for Circulating Tumor DNA Detection Based on Dual Signal Amplification.

Terahertz (THz) spectroscopy has impressive capability for label-free biosensing, but its utility in clinical laboratories is rarely reported due to often unsatisfactory detection performances. Here, we fabricated metal-graphene hybrid THz metasurfaces (MSs) for the sensitive and enzyme-free detection of circulating tumor DNA (ctDNA) in pancreatic cancer plasma samples. The feasibility and mechanism of the enhanced effects of a graphene bridge across the MS and amplified by gold nanoparticles (AuNPs) were investigated experimentally and theoretically. The AuNPs serve to boost charge injection in the graphene film and result in producing a remarkable change in the graded transmissivity index to THz radiation of the MS resonators. Assay design utilizes this feature and a cascade hybridization chain reaction initiated on magnetic beads in the presence of target ctDNA to achieve dual signal amplification (chemical and optical). In addition to demonstrating subfemtomolar detection sensitivity and single-nucleotide mismatch selectivity, the proposed method showed remarkable capability to discriminate between pancreatic cancer patients and healthy individuals by recognizing and quantifying targeted ctDNAs. The introduction of graphene to the metasurface produces an improved sensitivity of 2 orders of magnitude for ctDNA detection. This is the first study to report the combined application of graphene and AuNPs in biosensing by THz spectroscopic resonators and provides a combined identification scheme to detect and discriminate different biological analytes, including nucleic acids, proteins, and various biomarkers.

A novel ratiometric aptasensor based on SERS for accurate quantification of cardiac troponin I

Cardiac troponin I (cTnI) as a biomarker of acute myocardial infarction (AMI) is directly related to myocardial damage. Here, we proposed a ratiometric aptamer-sensor (aptasensor) for quantifying cTnI based on surface-enhanced Raman scattering (SERS), in which the uniform and high-density gold array was decorated with highly specific aptamer Tro4 to form the capture substrate for target cTnI. Firstly, gold array was labeled with 5, 5’-dithio bis-(2-nitrobenzoic acid) (DTNB) as one SERS signal to effectively realize signal self-calibration. In addition, aptamer Tro6 targeting cTnI and 4-mercaptobenzoic acid (4-MBA) as another SERS signal were anchored to porous gold (pAu) to form a pAu signal probe. In the presence of cTnI, the capture substrate and pAu signal probes could build a typical sandwich structure, thus the ratio of SERS peak intensity (I4-MBA/IDTNB) could be used to quantify cTnI. The ratiometric aptasensor showed a good linearity from 0.001 to 100 ng mL−1 and a low detection limit down to 0.27 pg mL−1. Own to dual signal output and the gold array substrate, the aptasensor exhibited good reproducibility, high sensitivity and accuracy. When the aptasensor was applied to the quantification of cTnI in human serum samples, the detection performance was comparable to that of enzyme-linked immunosorbent assay (ELISA), proving that the sensor has a good prospect in the diagnosis of AMI disease.

A double-enzyme cascade-responsive nanohydrogel for activatable photodynamic antibacterial therapy and dual fluorescence signal detection of bacterial infections

The tremendous morbidity and mortality caused by bacterial infections have emerged as a formidable menace to human health. The early detection and treatment of bacterial infections is imperative for effectively managing the progression of infectious diseases and mitigating infection-related mortality. In this study, we constructed a nanohydrogel consisting of cationic zinc phthalocyanine (CZP) and hyaluronic acid, which was further functionalized with a novel β-galactosidase detection probe, resulting in the formation of product CZP@HA:probe. The release of CZP and probe from CZP@HA:probe can be triggered by hyaluronidase, and the fluorescence of CZP and probe was turned on successively by hyaluronidase and β-galactosidase, respectively, demonstrating the dual enzyme-responsive property of CZP@HA:probe. CZP@HA:probe exhibited potent photodynamic killing activity against bacteria. The antibacterial mechanism potentially involved the generation of reactive oxygen species within bacteria and the disruption of the bacterial outer membrane. CZP@HA:probe had significant efficacy in promoting wound healing and exhibited a fluorescent indication of wound infections. The construction strategy of the nanohydrogel can be applied to other photosensitizers and probes, offering a novel perspective for the detection and treatment of bacterial infections.

Smartphone-based dual inverse signal MOFs fluorescence sensing for intelligent on-site visual detection of malachite green

The development of intelligent, sensitive, and visual methods for the rapid detection of veterinary drug residues is essential to ensure food quality and safety. Here, a smartphone-based dual inverse signal MOFs fluorescence sensing system was proposed for intelligent in-site visual detection of malachite green (MG). A UiO-66-NH2@RhB-dual-emission fluorescent probe was successfully synthesized in one step using a simple one-pot method. The inner filter effect (IFE) quenches the red fluorescence, while hydrogen bonding interaction enhances the blue fluorescence, enabling highly sensitive, accurate, and visual detection of MG dual inverse signals through fluorescence analysis. The probe showed great linearity over a wide range of 0.1–100 μmol/L, with a limit of detection (LOD) of 20 nmol/L. By integrating smartphone photography and RGB (red, green, and blue) analysis, accurate quantitative analysis of MG in water and actual fish samples can be achieved within 5 min. This developed platform holds great promise for the on-site detection of MG in practical applications, with the advantages of simplicity, cost-effectiveness, and rapidity. Consequently, it may open up a new pathway for on-site evaluation of food safety and environmental health.

Dual high-order QAM-modulated mm-wave signal transmission in the Q-band enabled by simple IM/DD architecture and bandpass delta-sigma modulation.

The intensity-modulation (IM)/direct-detection (DD) systems have been proven effective and low-cost due to their simple system architecture. However, the Mach-Zehnder modulator (MZM) of the IM/DD systems only reserves its driving signal intensity. Therefore, the IM/DD systems are generally unable to transmit vector signals and have a restricted spectrum efficiency and channel capacity. Similarly, the radio-over-fiber (RoF) transmission systems based on IM/DD are limited by their simple architecture and generally cannot transmit high-order quadrature amplitude modulation (QAM) signals, which hinders the improvement of their spectrum efficiency. To address the challenges, we propose a novel, to the best of our knowledge, scheme to simultaneously transmit the dual independent high-order QAM-modulated millimeter-wave (mm-wave) signals in the RoF system with a simple IM/DD architecture, enabled by precoding-based optical carrier suppression (OCS) modulation and bandpass delta-sigma modulation (BP-DSM). The dual independent signals can carry different information, which increases channel capacity and improves spectrum efficiency and system flexibility. Based on our proposed scheme, we experimentally demonstrate the dual 512-QAM mm-wave signal transmission in the Q-band (33-50 GHz) under three different scenarios: 1) dual single-carrier (SC) signal transmission, 2) dual orthogonal-frequency-division-multiplexing (OFDM) signal transmission, and 3) hybrid SC and OFDM signal transmission. We achieve high-fidelity transmission of dual 512-QAM vector signals over a 5 km single-mode fiber (SMF) and a 1-m single-input single-output (SISO) wireless link operating in the Q-band, with the bit error rates (BERs) of all three scenarios below the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10-3. To the best of our knowledge, this is the first time dual high-order QAM-modulated mm-wave signal transmission has been achieved in a RoF system with a simple IM/DD architecture.