A wide-color-varying ratiometric nanoprobe for detection of norepinephrine in urine samples

Plasmon-enhanced fluorescence sensor based on Au nanocages for sensitive detection of norepinephrine

BACKGROUND

Norepinephrine (NE) as a crucial monoamine neurotransmitter in the central and sympathetic nervous system, plays an important role in different physiological and pathophysiological processes. Brain NE can modulate cerebrospinal fluid flux and neurovascular coupling, regulate cortical and hippocampal neuronal circuitry, and participate the immune system. In addition, the reduced concentration of NE in brain was currently deemed to be the internal reason of major depression. However, development of detection method of NE with high spatiotemporal resolution in living systems remains a great challenge.

RESULTS

Herein, a plasmon-enhanced fluorescence (PEF) sensor based on Au nanocages (Aucages) were designed and prepared for ultra-sensitive detection of NE. Aucages with porous walls, hollow interior and systematically tunable localized surface plasmon resonance (LSPR) wavelengths (536 nm, 654 nm, 754 nm) were prepared to obtain a highly fluorescent enhancement of Au nanoclusters (Au NCs). Moreover, polyethylene glycol (PEG) with different molecular weight (1000, 5000, 10000 Da) were applied to control the distance between the Aucages and Au NCs. 3D-FDTD simulation results indicated that the fluorescence enhancement was primarily due to the internal and external enhanced electric field effects of Aucages. This sensor was applied for the turn-on detection of NE in commonly used clinical injectable norepinephrine bitartrate with the recovery rate of 98.06-105.34 %. Meanwhile, real-time fluorescence imaging of NE in living pheochromocytoma (PC-12) cells was explored with a red-emitted fluorescence.

SIGNIFICANCE

This study first employed Aucages with more "hot spot" for red-emitted Au NCs to realize fluorescence enhancement. It provides a new method for the development of more sensitive, accurate and convenient analysis of NE in clinical drug analysis, cell monitor and metabolism study.

A programmable paper-based microfluidic chip based on multicolor fluorescence carbon dots for visual sensing of multiple catecholamines in human serum

Catecholamines (epinephrine, norepinephrine, and levodopa) are a kind of neurotransmitter with similar structure, which orchestrates the regulation of emotional balance, stress adaptation, cardiovascular system optimization, and energy metabolism coordination. To satisfy the actual requirements for rapid, accurate, and on-site detection of multiple catecholamines, we propose a programmable paper-based microfluidic chip, which is loaded with diethanolamine as a multifunctional and efficient non-fluorescent detection probe. Specifically, diethanolamine reacts with epinephrine, norepinephrine, and levodopa to generate polymer carbon dots with yellow, green, and blue fluorescence. On this basis, the integration of paper-based microfluidics with smartphone-assisted technology enables the intelligent visual fluorescence detection of multiple catecholamines. The analytical device exhibits a good linear relationship in the detection of epinephrine (0.008 ~ 0.5 mM), norepinephrine (0 ~ 0.2 mM), and levodopa (0.004 ~ 0.06 mM), with lower limits of detection of 7.4, 19.6, and 1.6 μM, respectively. The practicability and efficiency of the analytical detection device were further demonstrated through the analysis of human serum samples. The intelligent analytical device for the individual quantitative detection and visual differentiation of epinephrine, norepinephrine, and levodopa provides a novel and exciting avenue for accurate detection of multiple catecholamines.

Simultaneous detection of norepinephrine and 5-hydroxytryptophan using poly-alizarin/multi-walled carbon nanotubes-graphene modified carbon fiber microelectrode array sensor

Multi-walled carbon nanotubes, graphene and alizarin polymer composites coated carbon fiber microelectrode array sensor (p-AZ/MWCNT-GR/CFMEA) was constructed and used for the simultaneous detection of norepinephrine (NE) and 5-hydroxytryptophan (5-HT). The morphology and structural characteristics of sensor are characterized using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Its electrochemical behavior has been studied with cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrochemical activity for the oxidation of NE and 5-HT, two well separated oxidation peaks with the peak potential difference of 220 mV are observed on the cyclic voltammogram. NE and 5-HT both show two electrons and two protons electrochemical reaction on the p-AZ/MWCNT-GR/CFMEA. Under the optimized experiment conditions, the linear ranges of the sensor for NE and 5-HT are 0. 08- 8 μM and 0. 1-20 μM with detection limits of 4. 22 nM and 14. 2 nM (S/N = 3), respectively. In addition, the microsensor array show good reproducibility, stability and selectivity for the determination of NE and 5-HT. Finally, the p-AZ/MWCNT-GR/CFMEA is applied to the simultaneous detection of NE and 5-HT in human serum samples and macrophages.

Fluorescent-Based Neurotransmitter Sensors: Present and Future Perspectives

Neurotransmitters (NTs) are endogenous low-molecular-weight chemical compounds that transmit synaptic signals in the central nervous system. These NTs play a crucial role in facilitating signal communication, motor control, and processes related to memory and learning. Abnormalities in the levels of NTs lead to chronic mental health disorders and heart diseases. Therefore, detecting imbalances in the levels of NTs is important for diagnosing early stages of diseases associated with NTs. Sensing technologies detect NTs rapidly, specifically, and selectively, overcoming the limitations of conventional diagnostic methods. In this review, we focus on the fluorescence-based biosensors that use nanomaterials such as metal clusters, carbon dots, and quantum dots. Additionally, we review biomaterial-based, including aptamer- and enzyme-based, and genetically encoded biosensors. Furthermore, we elaborate on the fluorescence mechanisms, including fluorescence resonance energy transfer, photon-induced electron transfer, intramolecular charge transfer, and excited-state intramolecular proton transfer, in the context of their applications for the detection of NTs. We also discuss the significance of NTs in human physiological functions, address the current challenges in designing fluorescence-based biosensors for the detection of NTs, and explore their future development.

Serotonin-Derived Fluorophore: A Novel Fluorescent Biomaterial for Copper Detection in Urine

We took advantage of the fluorescent features of a serotonin-derived fluorophore to develop a simple and low-cost assay for copper in urine. The quenching-based fluorescence assay linearly responds within the concentration range of clinical interest in buffer and in artificial urine, showing very good reproducibility (CV_av% = 4% and 3%) and low detection limits (16 ± 1 μg L^-1 and 23 ± 1 μg L^-1). The Cu²⁺ content was also estimated in human urine samples, showing excellent analytical performances (CV_av% = 1%), with a limit of detection of 59 ± 3 μg L^-1 and a limit of quantification of 97 ± 11 μg L^-1, which are below the reference value for a pathological Cu²⁺ concentration. The assay was successfully validated through mass spectrometry measurements. To the best of our knowledge, this is the first example of copper ion detection exploiting the fluorescence quenching of a biopolymer, offering a potential diagnostic tool for copper-dependent diseases.

Recent developments in polynorepinephrine: an innovative material for bioinspired coatings and colloids

While applications of polydopamine (PDA) are exponentially growing, research concerning the closely related neurotransmitter derivative polynorepinephrine (PNE) is in paucity, even though norepinephrine shares dopamine's ability to self-polymerize and form a coating film that is nearly substrate-agnostic. In this review, we demonstrate that PNE can be used as an alternative to PDA with equal or ever superior performance. PNE offers a thinner and smoother coating surface and thus is capable of more effectively resisting fouling by biofoulants, enhancing cell adhesion capability, surface hydrophilicity and biomolecule immobilisation. With the abundance of catechol, amino and hydroxyl groups in PNE's structure, PNE can perform as an electron donor and receiver at the same time and initiate ring opening and redox reactions. It has also been shown that PNE has the potential to be used as a biosensor due to its bioconjugation and molecular recognition ability. Here, we summarise the applications of PNE to date and discuss its potential research directions in the near future.

A Ratiometric Fiber Optic Sensor Based on CdTe QDs Functionalized with Glutathione and Mercaptopropionic Acid for On-Site Monitoring of Antibiotic Ciprofloxacin in Aquaculture Water

A ratiometric fluorescence fiber-optical sensor system (RFFS) merging a Y-type optical fiber spectrometer and CdTe QDs composite functionalized with glutathione and mercaptopropionic acid (GMPA@CdTe-QDs) for highly selective and on-site detection of ciprofloxacin (CIP) in environmental water samples was designed. Our preliminary results suggested that the red fluorescence of the synthesized GMPA@CdTe-QDs was effectively quenched by CIP. Based on this, the RFFS/GMPA@CdTe-QDs system was successfully fabricated and used for highly selective and rapid detection of CIP on site in the concentration range from 0 to 45 μM with the detection limit of 0.90 μM. The established method exhibited good interference resistance to the analogues of CIP and provided a great potential platform for real-time detection of CIP residues in environmental water. In addition, the fluorescence quenching mechanism of GMPA@CdTe-QDs by CIP was also investigated by means of temperature effect, fluorescence lifetime, ultraviolet (UV) visible absorption, and fluorescent spectra. Our results suggested clearly that the red fluorescence of GMPA@CdTe-QDs was quenched by CIP via the photoinduced electron-transfer (PET) mode.

Gold nanoparticles-based assays for biodetection in urine

Urine is a biofluid easy to collect through a non-invasive technique that allows collecting a large volume of sample. The use of urine for disease diagnosis is not yet well explored. However, it has gained attention over the last three years. It has been applied in the diagnosis of several illnesses such as kidney disease, bladder cancer, prostate cancer and cardiovascular diseases. In the last decade, gold nanoparticles (Au NPs) have attracted attention in biosensors' development for the diagnosis of diseases due to their electrical and optical properties, ability to conjugate with biomolecules, high sensitivity, and selectivity. Therefore, this article aims to present a comprehensive view of state of the art on the advances made in the quantification of analytes in urinary samples using AuNPs based assays, with a focus on protein analysis. The type of diagnosis methods, the Au NPs synthesis approaches and the strategies for surface modification aiming at selectivity towards the different targets are highlighted.

Application of NaYF4:Yb/Er/Tm UCNPs in Array-Based Sensing of Neurotransmitters: From a Single Particle to a Multichannel Sensor Array

A novel multichannel sensor array has been designed using a single, yet multiemissive lanthanide-doped upconversion nanoparticle (UCNP). The energy levels of lanthanide ions gave rise to several emission bands which were exploited as individual sensor elements for the recognition of four important neurotransmitters (NTs): dopamine, norepinephrine, levodopa, and serotonin. At alkaline conditions, the oxidation products of these NTs quenched the fluorescence emissions of UCNPs with different quenching degrees. The resulting fingerprint multichannel emission profiles from NaYF₄:Yb/Er/Tm UCNPs allowed the discrimination of NTs with excellent accuracy. The recognition was further verified in artificial cerebrospinal fluid, as a complex biological media. We believe that the designed UCNP-based multichannel sensor array offers innovative insights into the discrimination of various chemical signatures using a single measurement.

Norepinephrine as new functional monomer for molecular imprinting: An applicative study for the optical sensing of cardiac biomarkers

The continuous research for alternatives to antibody-based detection drove, in the last decades, the development of numerous strategies. Molecularly imprinted polymers (MIPs) emerged thanks to the low-cost and long-term stability features, where the choice of natural functional monomer(s) represents the key step for efficient imprinting of biomolecules. The chemical structure of dopamine (DA), one of the most used natural functional monomers, provided the inspiration for this work. We wondered why norepinephrine (NE) that differs from dopamine only for an additional hydroxyl group was not investigated at all in biosensing applications. In fact, there is only one paper exploiting polynorepinephrine (PNE) in molecular recognition applications, taking advantage of molecular imprinting, but not for biosensing purposes. In contrast, hundreds of papers describe polydopamine-based sensors. Therefore, we firstly investigated how the additional hydroxyl group of NE could affect the properties of the resulting polymer, and how these properties could be exploited for biosensing applications. The results highlighted the reduced non-specific adsorption of proteins onto PNE with respect to dopamine polymer. Furthermore, as a case study, we successfully developed a PNE-based imprinted biosensor for the early detection of Troponin I, a crucial biomarker for heart failure, by coupling the MIP biosensor with surface plasmon resonance (SPR) detection. The results indicate the feasible use of imprinted PNE as synthetic receptor for biomolecules, opening new perspectives for this biopolymer, so far not considered, and encouraging further investigations on its potential application in biosensing.

Ratiometric fluorescent nanoprobes for visual detection: Design principles and recent advances - A review

Signal generation techniques for visual detection of analytes have received a great deal of attention in various sensing fields. These approaches are considered to be advantageous when instrumentation cannot be employed, such as for on-site assays, point-of-care tests, and he althcare diagnostics in resource-constrained areas. Amongst various visual detection approaches explored for non-invasive quantitative measurements, ratiometric fluorescence sensing has received particular attention as a potential method to overcome the limitations of intensity-based probes. This technique relies on changes in the intensity of two or more emission bands (induced by an analyte), resulting in an effective internal referencing which improves the sensitivity of the detection. The self-calibration, together with the unique optophysical properties of nanoparticles (NPs) have made the ratiometric fluorescent nanoprobes more sensitive and reliable, which in turn, can result in more precise visual detection of the analytes. Over the past few years, a vast number of ratiometric sensing probes using nanostructured fluorophores have been designed and reported for a wide variety of sensing, imaging, and biomedical applications. In this work, a review on the NP-based ratiometric fluorescent sensors has been presented to meticulously elucidate their development, advances and challenges. With a special emphasis on visual detection, the most important steps in the design of fluorescent ratiometric nanoprobes have been given and based on different classes of analytes, recent applications of fluorescent ratiometric nanoprobes have been summarized. The challenges for the future use of the technique investigated in this review have been also discussed.

A facile and label-free ratiometric optical sensor for selective detection of norepinephrine by combining second-order scattering and fluorescence signals

In this work, a facile and label-free ratiometric sensor is constructed for selective determination of norepinephrine (NE) by coupling second-order scattering (SOS) and fluorescence, two different and independent optical signals. Herein, polyethyleneimine (PEI) dilute solution medium shows an intensive SOS signal without any fluorescence response. Interestingly, NE can be selectively induced by PEI to emit bright fluorescence, and meanwhile causes an observable decrease in the SOS signal due to the interactions between NE and PEI. The simultaneous variation of the two independent signals can be used for ratiometric sensing of NE. Under the optimal conditions, the resultant ratiometric sensor displays high sensitivity and selectivity toward NE by simultaneously monitoring fluorescence and SOS signals with the same excitation wavelength. The proposed sensor exhibits a good linear relationship versus NE concentration in the range of 10.0 nM-45.0 μM with a detection limit of 2.0 nM (S/N = 3) and has been successfully applied to the determination of NE in real samples without the use of any extra reagent. The combination of fluorescence and SOS signals provides a new scheme for ratiometric sensor design, greatly simplifying experimental procedure and effectively enhancing detection accuracy. Moreover, the proposed analytical strategy further broadens the application of dilute solutions of polymers in research into optical sensor and green analytical chemistry. Graphical abstract.

Poly(norepinephrine)-coated FeOOH nanoparticles as carriers of artemisinin for cancer photothermal-chemical combination therapy

The photothermal-chemical combination therapy is a promising approach for cancer treatment, however, chemotherapy often causes severe toxic and side effects on normal tissues. Herein, tumor-specific FeOOH@PNE-Art nanoparticles were fabricated via coating poly(norepinephrine) (PNE) on FeOOH nanoparticles, followed by loading of artemisinin (Art). The as-prepared nanoparticles exhibited excellent biocompatibility, strong near-infrared (NIR) absorbance and pH-responsive synchronous release of Art and iron ions. The released iron ions could not only supply iron ions in cancer cells which mediate endoperoxide bridge cleavage of Art and generate reactive oxygen species (ROS), but also react with H₂O₂ at tumour sites via the Fenton reaction and produce hydroxyl radicals, inducing a tumour-specific killing. Moreover, owing to the synchronous release of Art and iron ions as well as the low leakage of iron ions, FeOOH@PNE-Art nanoparticles showed extremely low toxicity to normal tissue. Under NIR light irradiation, the tumours in FeOOH@PNE-Art injected mice were thoroughly eliminated after 7 days of treatment and no tumour recurrence was found 30 days after treatment, manifesting very high efficacy of combination therapy.

Tumor-specific FeOOH@PNE-Art nanoparticles were fabricated that showed high efficacy of photothermal-chemical combination therapy and low toxicity to normal tissue.