Recent advances in chromophore-assembled upconversion nanoprobes for chemo/biosensing

Smartphone-assisted detection of trace methyl orange in water by ratiometric nanosensors based on down/up-conversion luminescence

A ratiometric nanosensor was developed for detecting methyl orange (MO) based on down/up-conversion luminescence achieved by a triplet-triplet annihilation upconversion luminescence (TTA-UCL) system. The probe, utilizing sensitizer and annihilator fluorophores encapsulated in nanomicelles, demonstrated high sensitivity and selectivity for MO detection. The energy transfer from UCL to MO endowed the sensor with responsive capabilities. The unaffected triplet-triplet energy transfer process maintained the phosphorescence signal constant, serving as a reference to construct the ratiometric sensor along with the UCL signal. Additionally, a smartphone-assisted colorimetric detection method was also developed based on the ratiometric sensor, enabling rapid and convenient detection of MO without the need for a spectrometer. The performance of the nanosensor in real water samples confirmed its potential for practical environmental applications.

Advances and Opportunities of luminescence Nanomaterial for bioanalysis and diagnostics

Luminescence nanomaterials (LNMs) have recently received great attention in biological analysis and sensing owing to their key advances in easy design and functionalization with high photostability, luminescence stability, low autofluorescence, and multiphoton capacity. The number of publications surrounding LNMs for biological applications has grown rapidly. LNMs based on Stokes and anti-Stokes shifts are powerful tools for biological analysis. Especially, unique properties of anti-Stokes luminescence such as upconversion nanoparticles (UCNPs) with an implementation strategy to use longer-wavelength excitation sources such as near-infrared (NIR) light can depth penetrate to biological tissue for bioanalysis and bioimaging. We observed that the LNMs-based metal-organic frameworks (MOFs) have been developed and paid attention to the field of bioimaging and luminescence-based sensors, because of their structural flexibility, and multifunctionality for the encapsulation of luminophores. This article provides an overview of innovative LNMs such as quantum dots (QDs), UCNPs, and LMOFs. A brief summary of recent progress in design strategies and applications of LNMs including pH and temperature sensing in biologically responsive platforms, pathogen detection, molecular diagnosis, bioimaging, photodynamic, and radiation therapy published within the past three years is highlighted. It was found that the integrated nanosystem of lab-on-a-chip (LOC) with nanomaterials was rapidly widespread and erupting in interest after the COVID-19 pandemic. The simple operation and close processes of the integration nanosystem together with the optimized size and low energy and materials consumption of biochips and devices allow their trend study and application to develop portable and intelligent diagnostics tools. The last part of this work is the introduction of the utilization use of LNMs in LOC applications in terms of microfluidics and biodevices.

Background-Free Imaging of Food Freshness Using Curcumin-Functionalized Upconversion Reversible Hydrogel Patch

Functionalized upconversion nanomaterials can overcome the drawbacks faced of strong background interference, photodamage, and spectral overlap by conventional optical labeling. Here, curcumin-functionalized upconversion hydrogel patch is designed with background-free and reversible for food freshness monitoring by ultra-sensitive response to biogenic amines. By loading the probes onto hydrogel patch, utilizing the good ductility to solve the problem of non-smooth surface coverage, thus accurately capturing biogenic amines. The presence of biogenic amines leads to the conversion of the diketone group on the probe to enolate ions, which triggers fluorescence resonance energy transfer (FRET) and ultimately causes the upconverted fluorescence to gradually change from green to red. The probe exhibits good detection capability for biogenic amines with a low limit of detection (LOD) of 2.73 µm. Interestingly, the patch can be restored to its initial state after water rinsing, realizing reversible detection of biogenic amines. Additionally, combining the color recognition system of smartphone can convert the imaging signal into a data signal to achieve quantitative analysis and show a reliable assessment comparable to the results of high performance liquid chromatography (HPLC). This study demonstrates the practical applicability in real-time monitoring of freshness, suggests great potential in developing optical nano-sensing strategy to ensure food safety.

A sharp and selective fluorescence paper-based sensor based on inner filter effect for ratiometric detection of four Sudan dyes in food matrix

The addition of Sudan dyes with carcinogenic effects to food threatens human health. Herein, a ratiometric fluorescence strip consisting of core-shell upconversion particles (NaYF4:Yb,Tm@NaYF4:Yb,Er), metal-organic frameworks and dual-template molecularly imprinted polymers was developed to selectively and sensitively detect four Sudan dyes based on inner filter effect (detection time only takes 8 min). The high adsorption capacity of metal-organic frameworks and the greater overlap between the emission of NaYF4:Yb,Tm@NaYF4:Yb,Er and the absorbance of four Sudan dyes enable the signal responses to be more sensitive. The limits of detection in chilli powder samples are as low as 29.87 ng/g, 37.55 ng/g, 47.89 ng/g and 51.02 ng/g, with satisfactory recovery (93.32-103.4%) and minor relative standard deviations (≤4.3%). This method broadens the idea for low-cost and portable detection of multiple illegal additives in complex substrates with high selectivity and sensitivity based on one kind of fluorescent strip.

A dual-mode fluorescence and colorimetric sensing platform for efficient detection of ofloxacin in aquatic products using iron alkoxide nanozyme

Trace detection of ofloxacin (OFL) with high sensitivity, reliability, and visual clarity is challenging. To address this, a novel dual-modal aptasensor with fluorescence-colorimetric capabilities was designed that exploit the target-induced release of 3,3',5,5'-tetramethylbenzidine (TMB) molecules from aptamer-gated mesoporous silica nanoparticles (MSNs), the oxidase-like activity of iron alkoxide (IA) nanozyme, and the fluorescence attributes of core-shell upconversion nanoparticles. Therefore, the study reports a dual mode detection, with a fluorescence detection range for OFL spanning from 0.1 μg/kg to 1000 μg/kg (and a detection limit of 0.048 μg/kg). Additionally, the colorimetric method offered a linear detection range of 0.3 μg/kg to 1000 μg/kg, with a detection limit of 0.165 μg/kg. The proposed biosensor had been successfully applied to the determination of OFL content in real samples with satisfactory recoveries (78.24-96.14 %).

Rapid detection of microalgae cells based on upconversion nanoprobes

The quantification of microalgae cells is crucial for the treatment of ships' ballast water. However, achieving rapid detection of microalgae cells remains a substantial challenge. Here, we develop a new method for rapid and effective detection of microalgae concentration by utilizing upconversion nanoprobes (UCNPs) of NaYF4:Er3+,Tm3+. Three ligands, carboxylated methoxypolyethylene glycols with 5000 and 2000 molecular weights (mPEG-COOH-5, mPEG-COOH-2) and D-gluconic acid sodium salt (DGAS), were used to convert hydrophobic UCNPs into a hydrophilic state through modification. The results show that the mPEG-COOH-5 modified UCNPs present the highest stability in an aqueous solution. Fourier Transform Infrared Spectroscopy (FTIR) measurements reveal the presence of a significant number of -COOH functional groups on UCNPs after the mPEG-COOH-5 modification. These -COOH groups enhance the hydrophilicity and biocompatibility of UCNPs. The soluble UCNPs were directly mixed with microalgae, and the upconversion luminescence (UCL) spectra of the UCNPs were recorded immediately after thorough shaking. This greatly reduces the measurement time and could realize rapid onboard detection. In this sensing procedure, the UCNPs with red UCL functioned as energy donors, while microalgae with red absorption served as an energy acceptor. The UCL gradually diminishes with an increase in microalgae concentration based on the inner filter effect, thus establishing a relationship between UCL and microalgae concentration. The accuracy of the detection is further validated through the traditional microscope counting method. These findings pave the way for a novel rapid strategy to assess microalgae concentration using UCNPs.

A Self-Accelerating Naphthalimide-Based Probe Coupled with Upconversion Nanoparticles for Ultra-Accurate Tri-Mode Visualization of Hydrogen Peroxide

The design and development of ultra-accurate probe is of great significance to chemical sensing in complex practical scenarios. Here, a self-accelerating naphthalimide-based probe with fast response and high sensitivity toward hydrogen peroxide (H2O2) is designed. By coupling with the specially selected upconversion nanoparticles (UCNPs), an ultra-accurate colorimetric-fluorescent-upconversion luminescence (UCL) tri-mode platform is constructed. Owing to the promoted reaction process, this platform demonstrates rapid response (< 1 s), an ultra-low detection limit (4.34 nM), and superb anti-interferent ability even in presence of > 21 types of oxidants, explosives, metallic salts, daily compounds, colorful or fluorescent substances. In addition, the effectiveness of this design is further verified by a sponge-based sensing chip loaded with the UCNPs/probe in recognizing trace H2O2 vapor from interferents with the three characteristic colors existing simultaneously. The proposed design of probe and tri-mode visualization detection platform is expected to open up a brand-new methodology for ultra-accurate sensing.

T790M mutation upconversion fluorescence biosensor via mild ATRP strategy and site-specific DNA cleavage of restriction endonuclease

A unique combination of a specific nucleic acid restriction endonuclease (REase) and atom transfer radical polymerization (ATRP) signal amplification strategy was employed for the detection of T790M mutations prevalent in the adjuvant diagnosis of lung cancer. REase selectively recognizes and cleaves T790M mutation sites on double-stranded DNA formed by hybridization of a capture sequence and a target sequence. At the same time, the ATRP strategy resulted in the massive aggregation of upconverted nanoparticles (UCNPs), which significantly improved the sensitivity of the biosensor. In addition, the UCNPs have excellent optical properties and can eliminate the interference of autofluorescence in the samples, thus further improving the detection sensitivity. The proposed upconversion fluorescent biosensor is characterized by high specificity, high sensitivity, mild reaction conditions, fast response time, and a detection limit as low as 0.14 fM. The performance of the proposed biosensor is comparable to that of clinical PCR methods when applied to clinical samples. This work presents a new perspective for assisted diagnosis in the pre-intervention stage of tumor diagnostics in the early stage of precision oncology treatments.

Highly sensitive detection for xanthine by combining single-band red up-conversion nanoparticles and cycle signal amplification strategy based on internal filtration effect

Up-conversion nanoparticles (UCNPs), especially single-band bright red UCNPs, have better penetration of biological tissues, absorb less lost energy, and have higher sensitivity and accuracy in the determination of actual biological samples in the field of biosensing. Here, a novel colorimetric and fluorescent dual-channel method based upon an internal filtration effect (IFE) quenching mechanism was proposed for the quantitative analysis of xanthine (XA) by using red UCNPs as fluorescence indicator and 3,3',5,5' -tetramethylbenzidine (TMB) as chromogenic substrate. The sensitivity of the detection system was also enhanced by a cycle signal amplification strategy based on the Fenton reaction. Under the best conditions, the detection limits of XA by fluorescent and colorimetric methods were 0.58 μM and 1.19 μM, respectively. The developed method was applied to the detection of XA in actual serum samples, and the recoveries of the spiked samples by fluorescent and colorimetric methods were in the range of 96.3-104.3 % and 94.3-105.4 %, respectively. In addition, the commercial ELISA method was used to verify the application of the proposed method and the test results of XA were close to those obtained by fluorescent and colorimetric methods, indicating that the accuracy of the developed nanosensing system was acceptable.

Highly sensitive and ratiometric detection of nitrite in food based on upconversion-carbon dots nanosensor

Nitrite (NO₂^-) is extensively found in the daily dietary environment. However, consuming too much NO₂^- can pose serious health risks. Thus, we designed a NO₂^--activated ratiometric upconversion luminescence (UCL) nanosensor which could realize NO₂^- detection via the inner filter effect (IFE) between NO₂^--sensitive carbon dots (CDs) and upconversion nanoparticles (UCNPs). Due to the exceptional optical properties of UCNPs and the remarkable selectivity of CDs, the UCL nanosensor exhibited a good response to NO₂^-. By taking advantage of NIR excitation and ratiometric detection signal, the UCL nanosensor could eliminate the autofluorescence thereby increasing the detection accuracy effectively. Additionally, the UCL nanosensor proved successful in detecting NO₂^- quantitatively in actual samples. The UCL nanosensor provides a simple as well as sensitive sensing strategy for NO₂^- detection and analysis, which is anticipated to extend the utilization of upconversion detection in food safety.

Ratiometric near-infrared upconversion fluorescence sensor for selectively detecting and imaging of Al3

Near-infrared (NIR) fluorescent probes provide extremely sensitive Al³⁺ detection for human health purposes. This research develops novel Al³⁺ response molecules (HCMPA) and NIR upconversion fluorescent nanocarriers (UCNPs), which respond to Al³⁺ through ratio NIR fluorescence. UCNPs improve photobleaching and visible light lack in specific HCMPA probes. Additionally, UCNPs are capable of ratio response, which will further enhance signal accuracy. The NIR ratiometric fluorescence sensing system has been successfully used to detect Al³⁺ within the range 0.1-1000 nM with an accuracy limit of 0.06 nM. Alternatively, a NIR ratiometric fluorescence sensing system integrated with a specific molecule can image Al³⁺ within cells. This study demonstrates that a NIR fluorescent probe is an effective and highly stable method of measuring Al³⁺ in cells.

NIR-excited imaging and in vivo visualization of β-galactosidase activity using a pyranonitrile-modified upconversion nanoprobe

β-galactosidase (β-gal) is a diagnostic biomarker of primary ovarian cancers. The development of effective fluorescent probes for investigating the activity of β-gal will be beneficial to cancer diagnosis. Herein, a near-infrared (NIR) excited ratiometric nanoprobe (DCM-β-gal-UCNPs) by assembling pyranonitrile dye (DCM-β-gal) on the surface of upconversion nanophosphors (UCNPs) was designed for the evaluation of β-gal activity in vivo. Upon the interaction with β-gal, a marked decrease of upconversion luminescence (UCL) signal in the green channel was observed owing to the luminescence resonance energy transfer from the UCNPs to pyranonitrile chromophore, whereas the NIR UCL emission at 800 nm was almost no influence. Thus, the β-gal activity could be quantitatively detected by the UCL intensity ratio of UCL_{543 nm}/UCL_{800 nm} with the limit of detection of 3.1 × 10^-4 U/mL. Moreover, DCM-β-gal-UCNPs was effectively applied for monitoring β-gal fluctuation in living cells and zebrafish by a ratiometric UCL signal excited by 980 nm laser. We envision that nanoprobe DCM-β-gal-UCNPs might be used as a potential bioimaging tool to disclose more biological information of β-gal in β-gal-associated diseases in the future.

NIR Photocontrolled Fluorescent Nanosensor under a Six-Branched DNA Nanowheel-Induced Nucleic Acid Confinement Effect for High-Performance Bioimaging

Although DNA nanotechnology is a promising option for fluorescent biosensors to perform bioimaging, the uncontrollable target identification during biological delivery and the spatially free molecular collision of nucleic acids may cause unsatisfactory imaging precision and sensitivity, respectively. Aiming at solving these challenges, we herein integrate some productive notions. On the one hand, the target recognition component is inserted with a photocleavage bond and a core-shell structured upconversion nanoparticle with a low thermal effect is further employed to act as the ultraviolet light generation source, under which a precise near-infrared photocontrolled sensing is achieved through a simple external 808 nm light irradiation. On the other hand, the collision of all of the hairpin nucleic acid reactants is confined by a DNA linker to form a six-branched DNA nanowheel, after which their local reaction concentrations are vastly enhanced (∼27.48 times) to induce a special nucleic acid confinement effect to guarantee highly sensitive detection. By selecting a lung cancer-associated short noncoding microRNA sequence (miRNA-155) as a model low-abundance analyte, it is demonstrated that the newly established fluorescent nanosensor not only presents good in vitro assay performance but also exhibits a high-performance bioimaging competence in live biosystems including cells and mouse body, propelling the progress of DNA nanotechnology in the biosensing field.

Deep-Depth Imaging of Hepatic Ischemia/Reperfusion Injury Using a Carbon Monoxide-Activated Upconversion Luminescence Nanosystem

Exploring a chemical imaging tool for visualizing the endogenous CO biosignaling molecule is of great importance in understanding the pathophysiological functions of CO in complex biological systems. Most of the existing CO fluorescent probes show excitation and emission in the region of ultraviolet and visible light, which are not suitable for application in in vivo deep-depth imaging of CO. Herein, a new near-infrared (NIR) to NIR upconversion luminescence (UCL) nanosystem for in vivo visualization of CO was developed, which possesses the merits of high selectivity and sensitivity, a deep tissue penetration depth, and a high signal-to-noise ratio. In this design, upon interaction with CO, the maxima absorption peak of the nanosystem showed a significant blue shift from 795 nm to 621 nm and triggered a remarkable turn-on NIR UCL signal due to the luminescence resonance energy transfer process. Leveraging this nanosystem, we achieved an NIR UCL visualization of the generation of CO biosignals caused by hypoxic, acute inflammation, or ischemic injury in living cells, zebrafish, and mice. Moreover, the protective effect of CO in zebrafish models of oxygen and glucose deprivation/reperfusion (OGD/R) and mice models of lipopolysaccharide-induced oxidative stress (LOS) and hepatic ischemia/reperfusion (HI/R) was also further verified. Therefore, this work discloses that the nanosystem not only serves as a promising nanoplatform to study biological signaling pathways of CO in pathophysiological events, but may also provide a powerful tool for HI/R injury diagnosis.

Upconverting nanoparticles based nanodevice for DNAzymes amplified miRNAs detection and artificially controlled chemo-gene therapy

Despite the great promise of cancer theranostic platforms, accurate diagnosis and effective treatment are still highly challenging. In this work, nanodevice for intracellular miRNAs detection and artificially controlled drug releasement was developed based on upconverting nanoparticles (UCNPs). For analysis aspect, DNAzymes amplified miRNA-21 detection was carried out, giving excellent sensitivity with detection limits of 1.8 × 10^-11 M. Moreover, intracellular fluorescence imaging permitted in situ diagnoses of miRNA-21 expression in living cells. Once the test identifies tumor markers, treatment can be performed. Here, artificially controlled chemo-gene synergetic therapy nanodevice was obtained by integrating UCNPs with photocleavable linkers (PC-linkers). In vitro and in vivo experiments verified the potential application of prepared nanodevice in cancer theranostics.