Ultrasensitive Probe Research Articles

PEGylated Ni Single-Atom Catalysts as Ultrasensitive Electrochemiluminescent Probes with Favorable Aqueous Dispersibility for Assaying Drug-Resistant Pathogens.

Ni single-atom catalysts (SACs) were synthesized by high-temperature calcination of nickel ions and 1,10-phenanthroline on carbon black as a carrier. Benefiting from the ultrahigh atom utilization efficiency, Ni SACs can significantly accelerate decay of dissolved oxygen to generate abundant reactive oxygen species through an oxygen reduction reaction occurring on cathodes. The generated reactive oxygen species can vastly enhance the electrochemiluminescent (ECL) signal of luminol without participation of exogenous co-reactants. To overcome the inherent unfavorable aqueous dispersibility of Ni SACs prepared by the calcination protocol, they were functionalized with highly hydrophilic PEG 2000. Thanks to the abundant carboxyl groups on PEG 2000, the PEGylated Ni SACs (Ni@PEG) can be used as ECL probes to tag biorecognition molecules. In this proof-of-principle work, an ECL biosensor for assaying methicillin-resistant Staphylococcus aureus was developed by using porcine IgG as capture molecule and phage cell-binding domain tagged with Ni@PEG as signal tracer. It shows a broad linear range of 73-7.3 × 106 CFU/mL and a low detection limit of 25 CFU/mL. The recovery values for assaying spiked samples are between 80.8 and 119.2%. It was also utilized to assess MRSA susceptibility to four antibiotics, with results consistent with those obtained by the standard broth microdilution technique. To the best of our knowledge, it is the first time to utilize aqueous dispersible SACs as highly sensitive ECL probes for developing biosensors.

Blue luminescent amino-functionalized graphene quantum dots as a responsive material for potential detection of metal ions and malathion

Large amounts of hazardous and toxic substances in the environment require non-toxic, cheap, easy, rapid, and sensitive methods for their detection. Blue luminescent graphene quantum dots (GQDs) were produced by electrochemical cleavage of graphite electrodes followed by gamma irradiation in the presence of ethylenediamine (EDA). Modified dots were able to detect metal ions (Co2+, Pd2+, Fe3+) due to photoluminescence quenching. The highest sensitivity was detected for the sample irradiated at a dose of 25 kGy. The limits of detection (LODs) were 1.79, 2.55, and 0.66 μmol L−1 for Co2+, Fe3+, and Pd2+, respectively. It was observed that GQDs irradiated at 200 kGy act as an ultra-sensitive turn-on probe for Malathion detection with LOD of 94 nmol L−1. Atomic force microscopy images proved the aggregation of GQDs in the presence of the investigated metal ions. Results obtained by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and LIVE/DEAD cytotoxicity test indicated that GQDs irradiated with EDA are not toxic towards MRC-5 cells, which makes them a promising, eco-friendly and safe material for sensing application.

Tyrosinase-functionalized gold nanoparticle-tailored ultrasensitive nanosensing probe for hazardous and nutritional phenolic compounds

Herein, a sensitive, selective, and facile sensing approach was developed by tailoring gold nanoparticles (AuNPs) to detect phenolic compounds in water and food/plant products across a range of concentrations. Sensing probes selective toward four different concentration ranges of phenolic compounds were constructed by varying the capping amounts (µg/mL) of tyrosinase (Ty) on the AuNP surface such as 5, 10, 50, and 100 µg/mL. Accordingly, an ultralow limit of detection (LOD) for phenolic compounds was achieved at 0.01 ppb (along with the upper bound detection of 50,000 ppm) via spectroscopic methodology. Interestingly, the absorbance of the developed sensing probe increased in the presence of phenolic compounds due to separation of Cu (present in Ty) from the proximity of AuNPs. A novel sensing mechanism has been proposed in light of interaction between enzyme substrate and copper of Ty with gold nanoparticles. Moreover, the applicability of the developed sensing probe is successfully validated using the tea leaves samples.

The Pivotal Role of Quantum Dots-Based Biomarkers Integrated with Ultra-Sensitive Probes for Multiplex Detection of Human Viral Infections.

The spread of viral diseases has caused global concern in recent years. Detecting viral infections has become challenging in medical research due to their high infectivity and mutation. A rapid and accurate detection method in biomedical and healthcare segments is essential for the effective treatment of pathogenic viruses and early detection of these viruses. Biosensors are used worldwide to detect viral infections associated with the molecular detection of biomarkers. Thus, detecting viruses based on quantum dots biomarkers is inexpensive and has great potential. To detect the ultrasensitive biomarkers of viral infections, QDs appear to be a promising option as biological probes, while physiological components have been used directly to detect multiple biomarkers simultaneously. The simultaneous measurement of numerous clinical parameters of the same sample volume is possible through multiplex detection of human viral infections, which reduces the time and cost required to record any data point. The purpose of this paper is to review recent studies on the effectiveness of the quantum dot as a detection tool for human pandemic viruses. In this review study, different types of quantum dots and their valuable properties in the structure of biomarkers were investigated. Finally, a vision for recent advances in quantum dot-based biomarkers was presented, whereby they can be integrated into super-sensitive probes for the multiplex detection of human viral infections.

Wavelength-multiplexed hook nanoantennas for machine learning enabled mid-infrared spectroscopy

Infrared (IR) plasmonic nanoantennas (PNAs) are powerful tools to identify molecules by the IR fingerprint absorption from plasmon-molecules interaction. However, the sensitivity and bandwidth of PNAs are limited by the small overlap between molecules and sensing hotspots and the sharp plasmonic resonance peaks. In addition to intuitive methods like enhancement of electric field of PNAs and enrichment of molecules on PNAs surfaces, we propose a loss engineering method to optimize damping rate by reducing radiative loss using hook nanoantennas (HNAs). Furthermore, with the spectral multiplexing of the HNAs from gradient dimension, the wavelength-multiplexed HNAs (WMHNAs) serve as ultrasensitive vibrational probes in a continuous ultra-broadband region (wavelengths from 6 μm to 9 μm). Leveraging the multi-dimensional features captured by WMHNA, we develop a machine learning method to extract complementary physical and chemical information from molecules. The proof-of-concept demonstration of molecular recognition from mixed alcohols (methanol, ethanol, and isopropanol) shows 100% identification accuracy from the microfluidic integrated WMHNAs. Our work brings another degree of freedom to optimize PNAs towards small-volume, real-time, label-free molecular recognition from various species in low concentrations for chemical and biological diagnostics.

Monitoring of circulating exosomal immuno checkpoint in tumor microenvironment through ultrasensitive aptamer-functionalized SERS probes

The exosomal programmed death ligand (PD-L1) and its combination with receptor PD-1 is pivotal in microtumor environment which favors the metastasis and impairs the natural immune system. We proposed a SERS-aptasensing techniques through which PD-L1 could be measured on circulating malignant exosomes by making it “sandwich” between CD63 targeting magnetic probes and PD-L1 targeting SERS tags. Accordingly, the aptasensor could quantify the PD-L1 with limit of detection (LOD) reaching 4.31 ag/mL. Interestingly, the SERS-aptasensor demonstrated much higher sensitivity than standard ELISA method in quantifying time-dependent PD-L1 variations in MC38 treated mice model. The viability of the SERS-aptasensor was further validated by analyzing raw serum samples using confocal and portable Raman systems which indicated 98% diagnostic accuracy. Collectively, our study reveals the ability of using aptamer-SERS method to quantify the PD-L1 in serum, suggesting an alternative promising strategy to monitor the efficacy of PD-L1/PD-1 immunotherapies.

Silver nanoparticle-coated polydopamine-copper hybrid nanoflowers as ultrasensitive surface-enhanced Raman spectroscopy probes for detecting thiol-containing molecules

In this study, silver nanoparticle-coated polydopamine-copper phosphate hybrid nanoflowers (Ag-PDA-Cu3(PO4)2 NFs) were synthesized and demonstrated to serve as efficient surface-enhanced Raman spectroscopy (SERS) probes for detecting thiol-containing molecules such as benzenethiol and thiocholine. Ag-PDA-Cu3(PO4)2 NFs were fabricated by forming PDA-Cu3(PO4)2 NFs through the nucleation of Cu3(PO4)2 on the PDA surface via interaction between Cu2+ and the free amine groups of dopamine, followed by the anisotropic growth of Cu3(PO4)2 crystals into flower-like microparticles. The NFs were then incubated with silver nitrate for in situ reduction to form Ag nanoparticles (NPs) on the surface of the NFs. The resulting hybrid NFs were demonstrated to act as SERS probes, sensitively detecting thiol-containing molecules, based on the successful interaction between Ag NPs and the thiol group (S-H) of the target molecules. The SERS intensities of benzenethiol and thiocholine at various concentrations were analyzed and found to yield superior limits of detection of 800 and 60 pM, respectively. Therefore, Ag-PDA-Cu3(PO4)2 NFs could be excellent SERS probes for detecting various thiol-containing molecules, particularly to determine the status of patients exposed to thiol-containing pesticides.

Ultrasensitive Fibroblast Activation Protein-α-Activated Fluorogenic Probe Enables Selective Imaging and Killing of Melanoma In Vivo.

Melanoma is a malignant cancer with a high risk of metastasis and continued increase in death rates over the past decades, and its prognosis is highly related to the disease's stage, while early detection and treatment of melanoma are significant to the improvement of its therapy outcome. Different from the traditional methods for disease diagnosis, enzyme-activated fluorescent probes were developed rapidly due to their high sensitivity and temporal-spatial ratio and have been widely applied in tumor detection, surgical navigation, and cancer-related research. Fibroblast activation protein-α (FAPα), a serine-type cell surface protease that plays important roles in cell invasion and extracellular matrix degradation, is widely involved in tumor progression such as malignant melanoma, so developing a FAPα activity-based molecular tool would be of great potential for the early diagnosis and therapy of melanoma. However, few fluorescent probes targeting FAPα have been applied in melanoma-related studies, and thus, the construction of FAPα activity-based fluorescent probes for melanoma detection is in urgent need. By incorporating the selective recognition unit with a red-emission fluorophore, cresyl violet, we herein report an ultrasensitive (limit of detection = 5.3 ng/mL) fluorogenic probe for FAPα activity sensing, named CV-FAP; the acquired probe showed a significantly higher binding affinity (15.7-fold) and overall catalytic efficiency (2.6-fold) when compared with those of the best reported FAPα probes. The good performance of CV-FAP made it possible to discriminate malignant melanoma cells and tumor-bearing mice from normal cells and mice with high contrast. More importantly, CV-FAP showed significant antitumor activity toward melanoma in cultured cells and tumor-bearing nude mice (over 95% inhibited tumor growth) with good safety, which made it an ideal theranostic agent for melanoma.

Cooperative Protonation Underlying the Acid Response of Metal–Organic Frameworks

Cooperative binding plays essential roles in many biochemical processes and has important implications for the development of sensory materials. Metal–organic frameworks (MOFs) can be designed to possess multiple binding sites on pore surfaces, but binding cooperativity within the confined space is rarely recognized. Here, we present a systematic study on cooperative protonation in MOFs in order to gain structural insights into the phenomenon. Three microporous Zr(IV) MOFs were studied for comparison, two furnished with sterically hindered but proton-accessible sites (Zr-PTB and Zr-PPTB) and one free of pyridyl sites (Zr-BTB, isostructural to Zr-PTB). Zr-PTB and Zr-PPTB show two opposite and simultaneous fluorescence transitions in narrow pH changes, which has the appeal for ultrasensitive pH probing. The dual-emission response is ascribable to pyridyl protonation, which turns off the (n, π*) emission and, meanwhile, turns on the (π, π*) emission. The abrupt fluorescence transitions arise from positive cooperativity of multisite protonation. Zr-PPTB shows stronger cooperativity (Hill coefficient h = 1.6) than Zr-PTB (h = 1.2). Structural inspection suggests that the arrangement of the pyridyl sites in Zr-PPTB is conducive to the interplay between pyridyl sites. Moreover, we demonstrate abrupt enhancement (up to 500 times) in proton conduction for Zr-PTB below the pH of cooperative protonation, with a maximum conductivity of 1.2 × 10–2 S cm–1 at 347 K and 98% RH. Zr-PPTB also shows abrupt conductivity enhancement upon cooperative protonation, but the enhancement is smaller. We ascribe the difference to the biased allocation of pyridyl sites between different channels of Zr-PPTB.

Enhanced Ultrasensitive Photoelectrochemical Probe for Phosphate Detection in Water Based on a Zirconium-Porphyrin Framework.

Excessive phosphate poses a serious ecological and human health risk, and thereby, monitoring its trace concentration is of great significance to environmental protection and human health. In this work, a zirconium-porphyrin framework (PCN-222) with excellent stability and unique luminescence properties was designed to modify the surface of the indium tin oxide electrode, which was first used as a photoelectrochemical (PEC) probe for phosphate detection. The PCN-222-modified PEC probe demonstrated an excellent selectivity and stability and indicated a linear response to phosphate in the range of 0-106 nM with a limit of detection (LOD) as low as 1.964 nM. To the best of our knowledge, this is the phosphate probe with the lowest LOD, and this is also the first signal-on PEC probe toward phosphate based on PCN-222. More importantly, the PEC probe can be validated for the good applicability of trace phosphate detection in real water samples, indicating a good application prospect. Finally, a series of electrochemical and spectroscopic studies have proved that phosphate can bind to the indium tin oxide (ITO)/PCN-222 electrode, which shortens the distance of the space charge region while reducing the bandwidth and thus facilitates the transfer of photogenerated electrons across the energy band barrier to reduce O2 in the electrolyte, producing an enhanced cathodic photocurrent signal. The proposed strategy of the highly sensitive PEC probe provides a promising platform for more effective label-free phosphate monitoring in the environment and organisms.

Ratiometric photothermal detection of silver ions using diimmonium salts.

Selective detection and determination of silver ions are tricky due to the poor reactivity and the interference of various metal ions and halides. Only a few cases have been reported concerning sulfur-based functionality. This work proposes silver-selective probes exhibiting peculiar colorimetric and photothermal responses without the need for sulfur-functional groups. Tetrakis(4-dialklyaminophenyl)1,4-phenylenediamine containing hexyl and methoxytriethyleneglycol substituents, PTS1 and PTS2, respectively, are selectively oxidized by silver ions to form dicationic diimmonium salts. The resulting quinone diimminium salts show strong absorption in the near-infrared (NIR) region with intense color changes. The striking color change is observed from pale brown to intense olive green with immediate responses. PTS1 shows a higher binding constant and nanomolar detection limit, whereas PTS2 shows a sub-micromolar detection limit. Job's plot studies reveal the stoichiometric ratio as 1:2 (PTS1: Ag+). Due to the strong NIR absorption of the oxidized PTS probes, the temperature rise is monitored, after adding silver ions, by a thermal camera and in-contact thermal sensors. The concentration of the actual samples can be determined based on a calibration plot with a temperature change as a function of silver ion concentration. The current results offer highly selective and ultrasensitive probes for silver ions under multiple detection mediums, including naked eye and photothermal detection.

De novo design of an ultrasensitive fluorogenic probe for aminopeptidase N sensing in living system

Aminopeptidase N is a widely expressed zinc-biding metalloprotease which plays important roles in maintaining normal physiological functions and the abnormal activity of APN is highly related chronic inflammatory disease and cancer progression. Thus, the detection and specific tracing of APN activity is of great importance in clinical diagnosis, drug discovery and disease related biological study. To date, enzyme activated fluorescent probe has attracted intense attention due to its high sensitivity and spatial-temporal resolution and biocompatibility in living system. Many researchers have attempted in constructing APN activity based probes and applicated in medical study such as tumor imaging, photodynamic therapy, and surgical navigation. However, these probes were all acquired by incorporating the fluorophore with its natural substrate. Thus, to discovery a new design strategy for APN targeting could provide efficient alternative method for APN probe construction and APN related chemical biology research. By adapting the unnatural amino-acid (2-Aminobutyric acid, Abu) which showed high affinity and specificity toward APN, we herein proposed a new probe design strategy for APN sensing and a near-infrared fluorescent probe TMN-Abu was constructed through this strategy. The in vitro assays showed that TMN-Abu possess high sensitivity toward APN (LOD = 0.57 ng/mL) and high binding affinity toward APN (Km = 19.1 ± 1.84 μM). Most importantly, TMN-Abu was successfully applicated into monitoring endogenous APN activity in living cells, tumor-bearing nude mice and for the first time applicated into diabetic model mice and APN activity dynamic change in biological events such as starvation and EGF stimulation.

Recent Developments of Nanodiamond Quantum Sensors for Biological Applications.

Measuring certain quantities at the nanoscale is often limited to strict conditions such as low temperature or vacuum. However, the recently developed nanodiamond (ND) quantum sensing technology shows great promise for ultrasensitive diagnosis and probing subcellular parameters at ambient conditions. Atom defects (i.e., N, Si) within the ND lattice provide stable emissions and sometimes spin‐dependent photoluminescence. These unique properties endow ND quantum sensors with the capacity to detect local temperature, magnetic fields, electric fields, or strain. In this review, some of the recent, most exciting developments in the preparation and application of ND sensors to solve current challenges in biology and medicine including ultrasensitive detection of virions and local sensing of pH, radical species, magnetic fields, temperature, and rotational movements, are discussed.

High-fidelity imaging of amyloid-beta deposits with an ultrasensitive fluorescent probe facilitates the early diagnosis and treatment of Alzheimer's Disease.

Background: Imaging amyloid-beta (Aβ) deposits with high fidelity in naturally aging brains is crucial for the early diagnosis of Alzheimer's disease (AD). However, this is impeded by the lack of highly sensitive probes.Methods: By conducting computational modelling to quantitatively fine-tune the twisted intramolecular charge transfer (TICT) tendency of Thioflavin T (ThT) analogues, we developed an ultrasensitive probe AH-2. AH-2 retained the binding affinity and binding mode of ThT towards Aβ deposits, and exhibited ca 10-fold less background fluorescence and 5-10 folds of improved signal-to-background contrast upon binding Aβ deposits. These desirable features endowed AH-2 the sensitivity to detect Aβ deposition in naturally aging wild-type mice.Results: AH-2 imaging revealed that Aβ puncta signals appeared near the nuclei in young mice and spread through the intracellular and extracellular compartments in older mice. Moreover, Aβ deposits were observed to emerge earlier in mice cerebral cortex than in the hippocampus region. Given this desirable sensitivity and good spatiotemporal resolution, AH-2 was successfully applied in the preclinical evaluation of Aβ-targeted treatment by melatonin.Conclusions: We expect that AH-2 is promising for early diagnosis of AD and will serve as a sensitive tool for studying Aβ-related AD pathology.

Laser Spectroscopic Tools for Nano-Biophotonics

Biophotonics is a vibrant interdisciplinary field exploring the interaction between electromagnetic radiation and biological materials such as sub-cellular structures and molecules in living organisms. Biophotonics research leads to applications in agriculture and life sciences and produces tools for medical diagnostics and therapies. Working in this general field, we have recently made advances toward ultrasensitive Raman-spectroscopic probing of viruses. Our approach is based on laser spectroscopy aided by plasmonic nanoantennas, as in tip-enhanced Raman spectroscopy (TERS). An additional enhancement in sensitivity and speed is obtained by employing the femtosecond adaptive spectroscopic technique (FAST) for coherent anti-Stokes Raman scattering (CARS). The combined approach shows promise for non-destructive label-free bioimaging with molecular-level sensitivity and with spatial resolution down to a fraction of a nanometer.

Nanostructured carbon-fiber surfaces for improved neurochemical detection.

Fundamental insight into the extent to which the nanostructured surface and geometry impacts neurochemical interactions at electrode surfaces could provide significant advances in our ability to design and fabricate ultrasensitive neurochemical detection probes. Here, we investigate the extent to which the nanostructure of the carbon-fiber surface impacts detection of catecholamines and purines with fast-scan cyclic voltammetry (FSCV). Carbon-fibers were treated with argon (Ar) plasma to induce variations in the nano- and micro-structure without changing the functionalization of the surface. We tested variations in topology by measuring the extent to which the flow rate, RF power, and treatment time affect the surface roughness. Flow rates from 50-100 sccm, plasma power from 20-100 W, and treatment times from 30 s to 5 min were compared. Two Ar-treatments were chosen from the optimization studies for comparison, and the surface roughness was evaluated using atomic force microscopy (AFM). To ensure no changes in chemical composition, fibers were analyzed with X-ray photoelectron spectroscopy (XPS). On average, at the optimized Ar-plasma treatment procedure, oxidative current for adenosine and ATP increased by 3.5 ± 1.4-fold and 3.2 ± 0.6-fold, and guanosine and GTP by 1.7 ± 0.3-fold and 1.8 ± 0.3-fold, respectively (n = 9). Dopamine increased by 1.7 ± 0.3-fold. The extent to which changes in the electrode structure impact adsorption, sensitivity, and electron transfer rates were measured. A COMSOL Multiphysics simulation was developed to enable the modeling of mass transport of electroactive species at varying electrode geometries. Overall, this study provides critical insight into the extent to which the nanostructure of the surface impacts the electrochemical detection of neurochemicals.

Acridine-based dyes as high-performance near-infrared Raman reporter molecules for cell imaging.

A surface-enhanced Raman scattering (SERS) nanoprobe has been proven to be a promising tool for near-infrared (NIR) biomedical imaging and diagnosis because of its high sensitivity and selectivity. However, the development of NIR SERS reporters has been a bottleneck impeding the preparation of ultrasensitive SERS probes. Herein, we report the design and synthesis of a series of SERS reporters in the NIR region based on 10-methylacridine (AD). The AD nanotags (gold nanostar–AD molecules–BSA, AuNS–AD–BSA) exhibit appreciable SERS signals and can be detected at as low as the sub-picomole level. The results of in vitro imaging experiments show that it can be used in live-cell delineation.

Ultrasensitive Fluorogenic Probe for Detecting Ferrous Ion in Parkinson's Disease Models Using Paper-Based Fluorescent Sensor and Two-Photon Fluorescence Microscopy

Ultrasensitive Fluorogenic Probe for Detecting Ferrous Ion in Parkinson's Disease Models Using Paper-Based Fluorescent Sensor and Two-Photon Fluorescence Microscopy

Ultra-Sensitive Fluorometric and Colorimetric Probes for Β-Glucuronidase-Triggered Generation of Silicon Nanoparticles as Dual Mode Assay

Ultra-Sensitive Fluorometric and Colorimetric Probes for Β-Glucuronidase-Triggered Generation of Silicon Nanoparticles as Dual Mode Assay

Ultrasensitive chemiluminescent neuraminidase probe for rapid screening and identification of small-molecules with antiviral activity against influenza A virus in mammalian cells.

Influenza A virus is the most virulent influenza subtype and is associated with large-scale global pandemics characterized by high levels of morbidity and mortality. Developing simple and sensitive molecular methods for detecting influenza viruses is critical. Neuraminidase, an exo-glycosidase displayed on the surface of influenza virions, is responsible for the release of the virions and their spread in the infected host. Here, we present a new phenoxy-dioxetane chemiluminescent probe (CLNA) that can directly detect neuraminidase activity. The probe exhibits an effective turn-on response upon reaction with neuraminidase and produces a strong emission signal at 515 nm with an extremely high signal-to-noise ratio. Comparison measurements of our new probe with previously reported analogous neuraminidase optical probes showed superior detection capability in terms of response time and sensitivity. Thus, as far as we know, our probe is the most sensitive neuraminidase probe known to date. The chemiluminescence turn-on response produced by our neuraminidase probe enables rapid screening for small molecules that inhibit viral replication through different mechanisms as validated directly in influenza A-infected mammalian cells using the known inhibitors oseltamivir and amantadine. We expect that our new chemiluminescent neuraminidase probe will prove useful for various applications requiring neuraminidase detection including drug discovery assays against various influenza virus strains in mammalian cells.