Fluorescent nanoparticles for chemical and biological sensing

A highly sensitive and selective fluorescent biosensor for breast cancer derived exosomes using click reaction of azide-CD63 aptamer and alkyne-polymer dots

Exosomes have gained recognition as valuable reservoirs of biomarkers, holding immense potential for early cancer detection. Consequently, there is a pressing need for the development of an economical and highly sensitive exosome detection methodology. In this work, we present a fluorescence method for breast cancer-derived exosome detection based on Cu-triggered click reaction of azide-modified CD63 aptamer and alkyne functionalized Pdots. The detection threshold for the exosomes obtained from the breast cancer serum was determined to be 6.09 × 107 particles per μL, while the measurable range spanned from 6.50 × 107 to 1.30 × 109 particles per μL. The employed methodology achieved notable success in accurately distinguishing breast cancer patients from healthy individuals through serum analysis. The application of this method showcases the significant potential for early exosome analysis in the clinical diagnosis of breast cancer patients.

Photophysical properties of fluorescent nucleobase P-analogues expected to monitor DNA replication

In this work, we computationally design a series of fluorescent purine analogues based on the 2-amino-8-(1'-β-D-2'-deoxyribofuranosyl)-imidazo[1,2-a]-1,3,5-triazin-4(8H)-one (P) to monitor the DNA replication process with merely a minimal perturbation to the natural structure of nucleic acid. The P-modified fluorescent probes present red-shifted absorption spectra and enhanced photoluminescence due to the additional π-conjugation resulting from the fluorophore modification and the ring-expansion. Efficient fluorescence quenching of P-analogues occurs upon pairing with the complementary 6-amino-5-nitro-3-(1'-β-D-2'-deoxyribofuranosyl)-2(1H)-pyridone (Z) due to the nonradiative relaxation from the low-lying dark excited state to the ground state of Z moiety. Especially, the P3 and the P7, which have high fluorescence intensity in both gas and liquid phases, are proposed as the sensors for studying conformational switching in the presence and absence of a complementary sequence. Also examined are the influences of hydration and the linking to deoxyribose on absorption and emission processes. Besides, the potential phosphorescence emission of these modified base pairs is taken into account by constructing the relaxed potential energy curves of S₀, T₁ and S₁ states.

Application of dendrimer-based nanosensors in immunodiagnosis

Conventional immunoassays such as ELISA and FLISA have been used for clinical diagnosis for a long time. These assays are complex, time-consuming, and uneconomical. They have been overwhelmed with newer and more efficient methods such as electrochemical and electrochemiluminescent immunosensors that are cost-effective and require less time. Immunosensor is a biosensor that consists of a signal transducer and a biologically interactive system such as antigen and antibody interaction. Recent advances in nanotechnology have seen numerous efforts towards the usage of nanoparticles such as dendrimers in immunoassays. Dendrimers are highly branched structures with a high density of active peripheral groups, expanding their wide range of applications in immunoassays. A vast number of peripheral groups enrich the sensitivity of the immunosensor by governing the orientation of the antibody on the sensor surface. The current review highlights recent progress and developments in applying dendrimers for different immunoassays and their applicability in analyzing various biomarkers in clinical disease diagnosis.

Highly Selective and Sensitive Aggregation-Induced Emission of Fluorescein-Coated Metal Oxide Nanoparticles

We report the synthesis, characterization, and photophysical properties of novel metal oxide nanoparticles (NPs) coated with specially designed fluorescein substituents which are capped with electron-withdrawing groups. The fluorescein-coated nanoparticles were synthesized in excellent yields, and their structures were confirmed using various advanced spectroscopic, instrumental, and surface analysis techniques, revealing the formation of the target functionalized nanoparticles (FNPs) which show superior chemical and thermal stabilities. In addition, the photophysical properties of the FNPs were examined using UV-visible absorption and fluorescence spectroscopy. These latter techniques disclosed aggregation-induced emission (AIE) properties for most of the target FNPs, namely those which are soluble in common organic solvents at selective concentration ranges of water fractions in the solvent mixture.

A Novel Fluorescence and SPE Adsorption Nanomaterials of Molecularly Imprinted Polymers Based on Quantum Dot-Grafted Covalent Organic Frameworks for the High Selectivity and Sensitivity Detection of Ferulic Acid

A fluorescence and solid phase extraction (SPE) adsorption nanomaterials of molecularly imprinted polymers (MIPs) based on quantum dot-grafted covalent organic frameworks (QD-grafted COFs) was prepared by one-pot surface-imprinting synthesis method. Amino groups of silane reagent were at the surface of QDs to coordinate COFs efficiently by Schiff-base reactions, providing thermal and chemical stability to MIPs. It also reacted with the phenolic hydroxyl groups of ferulic acid (FA) through non-covalent interactions. The nanomaterials were used as fluorescence sensing and SPE adsorption toward determination of ferulic acid. The MIPs based on QD-grafted COFs had good fluorescence response ability, and quenching linearly at concentrations of ferulic acid from 0.03 to 60 mg kg^-1, with a detection limit of 5 µg kg^-1. At the same time, it exhibited a good SPE adsorption ability, and the FA extraction was from 1.63 to 3.11 mg kg^-1 in grain by-products by SPE coupled with high performance liquid chromatography/mass spectrometry (HPLC/MS). The fluorescence and SPE-HPLC/MS were used for the efficient detection of ferulic acid in real samples with recovery values of 88⁻114% and 90⁻97%, respectively. Furthermore, the nanomaterials of MIPs based on QD-grafted COFs were used for FA detection with high sensitivity and selectivity, and it also increased the recycling of waste resources.

Facile Fabrication of Fluorescent Inorganic Nanoparticles with Diverse Shapes for Cell Imaging

In the present work, we describe a facile and general method of fabricating fluorescent inorganic nanoparticles with diverse shapes for cell imaging application. The hematite (α-Fe₂O₃) nanoparticles (HNPs) with three different shapes (i.e., spindle shape, ellipsoidal shape and quasi-spherical shape) were first prepared as model systems in consideration of good biocompatibility and the controllable morphology of α-Fe₂O₃. Three fluorescent HNPs with different shapes were readily achieved via one-pot sol-gel reaction of AIE luminogen-functionalized siloxane (AIEgen-Si(OCH₃)₃) and TEOS in the presence of PVP-stabilized HNPs. Due to the fluorescence originating from the thin AIEgens-contained SiO₂ shell around the HNPs, their photoluminescent intensities can be tuned by changing the concentrations of TEOS and AIEgen-Si(OCH₃)₃ in feed prior to the sol-gel reaction. When the as-prepared fluorescent products were dispersed in water, they gave intense green light emission upon excitation at 360 nm with relatively high fluorescence quantum yield. Further, fluorescent HNPs exhibited low cytotoxicity and excellent photostability and, thus, were used as optical probes to preliminarily explore the effect of nanoparticle shapes on their cellular uptake behaviors. This work should open a facile way to prepare various fluorescent inorganic nanoparticles with specific morphology for various biological applications.

Stimulus responsive nanogel with innate near IR fluorescent capability for drug delivery and bioimaging

A brighter, non toxic and biocompatible optical imaging agent is one of the major quests of biomedical research. Here in, we report a photoluminescent comacromer [PEG-poly(propylene fumarate)-citric acid-glycine] and novel stimulus (pH) responsive nanogel endowed with excitation wavelength dependent fluorescence (EDF) for combined drug delivery and bioimaging applications. The comacromer when excited at different wavelengths in visible region from 400nm to 640nm exhibits fluorescent emissions from 510nm to 718nm in aqueous condition. It has high Stokes shift (120nm), fluorescent lifetime (7 nanoseconds) and quantum yield (50%). The nanogel, C-PLM-NG, prepared with this photoluminescent comacromer and N,N-dimethyl amino ethylmethacrylate (DMEMA) has spherical morphology with particle size around 100nm and 180nm at pH 7.4 (physiological) and 5.5 (intracellular acidic condition of cancer cells) respectively. The studies on fluorescence characteristics of C-PLM NG in aqueous condition reveal large red-shift with emissions from 523nm to 700nm for excitations from 460nm to 600nm ascertaining the EDF characteristics. Imaging the near IR emission with excitation at 535nm was accomplished using cut-off filters. The nanogel undergoes pH responsive swelling and releases around 50% doxorubicin (DOX) at pH 5.5 in comparison with 15% observed at pH 7.4. The studies on in vitro cytotoxicity with MTT assay and hemolysis revealed that the present nanogel is non-toxic. The DOX-loaded C-PLM-NG encapsulated in Hela cells induces lysis of cancer cells. The inherent EDF characteristics associated with C-PLM NG enable cellular imaging of Hela cells. The studies on biodistribution and clearance mechanism of C-PLM-NG from the body of mice reveal bioimaging capability and safety of the present nanogel. This is the first report on a polymeric nanogel with innate near IR emissions for bioimaging applications.

Sandwich Immunoassays of Multicomponent Subtrace Pathogenic DNA Based on Magnetic Fluorescent Encoded Nanoparticles

A novel magnetic fluorescent encoded nanoimmunoassay system for multicomponent detection and separation of the subtrace pathogenic DNA (hepatitis B virus surface gene, HBV; hepatitis A virus poly the protein gene, HAV) was established based on new type of magnetic fluorescent encoded nanoparticles and sandwich immunoassay principle. This method combines multifunctional nanoparticles, immunoassay technique, fluorescence labeling, and magnetic separation of multicomponent technology. It has many advantages such as high sensitivity, low detection limit, easy operation, and great potential for development. The results of this work show that, based on nanoimmunoassay system, it could quantitatively detect the multicomponent trace pathogenic HAV and HBV DNA, as well as detection limit up to 0.1 pM and 0.12 pM. Furthermore, with the improvement of the performances of magnetic fluorescent encoded nanoparticles, the sensitivity will be further improved. In this experiment, a new nanoimmunoassay system based on magnetic fluorescent encoded nanoparticles was established, which will provide a new way for the immunoassay and separation of multicomponent biomolecules.

Fabrication of hybridized nanoparticles with aggregation-induced emission characteristics and application for cell imaging

More TPE-CS/HA nanoparticles are endocytosed by culture for a long time, resulting in a much stronger fluorescence emission.

Facile and large scale in situ synthesis of the thermal responsive fluorescent SiNPs/PNIPAM hydrogels

A new type of F-SiNPs/poly(N-isopropylacrylamide) (F-SiNPs/PNIPAM) hydrogel was prepared byin situpolymerization. The composite hydrogels display visible thermal-sensitive phase transition properties.

Trace detection of nitro aromatic explosives by highly fluorescent g-C3N4 nanosheets

Highly fluorescent g-C3N4 nanosheets were facilely fabricated by exfoliating bulk g-C3N4 under ultrasonic irradiation for 1 h. The atomic force microscopy (AFM) image shows that the resultant g-C3N4 nanosheets are ∼6-14 nm thick, and the suspension is stable in air for several weeks. Remarkably, the obtained nanosheets exhibited strong fluorescence with an extremely high quantum yield (QY) up to 32%, and high sensitivity, selectivity, as well as a fast response to nitro aromatic explosives were observed. Typically, the quenching efficiency coefficient Ksv for PNP was 30,460 M(-1), which proved that the resultant nanosheets possessed an extremely high sensitivity for nitro-phenol PNP detection.

Strongly fluorescent organogels and self-assembled nanostructures from pyrene coupled coumarin derivatives: application in cell imaging

The present work reports facile synthesis of pyrene coupled coumarin derivatives which could form self-assembled molecular gel and nano-flakes. The nanomaterials obtained via a self-assembly process could be potentially used in fluorescence imaging applications.

Protein-templated gold nanoclusters sequestered within sol-gel thin films for the selective and ratiometric luminescence recognition of Hg2+

Sequestration of bovine serum albumin (BSA)-stabilized gold nanoclusters (AuNCs@BSA) prepared using microwave assistance within sol-gel-derived mesoporous silica films permits the selective and highly sensitive quenchometric detection of aqueous Hg(2+) (limit of detection = 600 pM) with luminescence signal arising from oxidized BSA allowing for an analytically robust and reliable ratiometric detection. Overall, this work highlights a number of important advances, including the highest luminescence quantum yield reported to date for a protein-templated luminescent noble metal nanocluster (13%) made possible using a microwave-mediated synthesis followed by cold incubation. We also demonstrate the clear advantage of exploiting the luminescence signal arising from oxidized BSA as an internal reference to generate selectivity of response to Hg(2+). A careful Stern-Volmer quenching analysis reveals the persistence of two unique quenching sites for AuNCs@BSA entrapped within a sol-gel-derived glass, a minor population of which is unquenchable. Finally, based on these AuNCs@BSA nanosensors, we advise a path forward for paper-based indicator strip detection of heavy metals in aqueous streams, the implementation of which can be performed using the unaided eye, making it a meaningful approach for routine screening and in resource-limited situations.

Recent advances in fluorescent nucleic acid probes for living cell studies

Living cell studies can offer tremendous opportunities for biological and disease studies. Due to their high sensitivity and selectivity, minimum interference with living biological systems, ease of design and synthesis, fluorescent nucleic acid probes (FNAPs) have been widely used in living cell studies, such as for intracellular detection, cell detection, and cell-to-cell communication. Here, we review the general requirements and the recent developments in FNAPs for living cell studies. We broadly classify these designs as hybridization probes and aptamer probes. For hybridization probes, we describe recently developed designs, such as nanomaterial-based and amplification-based hybridization probes. For aptamer probes, we discuss four general paradigms that have appeared most frequently in the literature: nanomaterial-based, nanomachine-based, cell surface-anchored and activatable aptamer probe designs in vivo. FNAPs promise to open up new and exciting opportunities in biological marks detection for a wide range of biological and medical applications.

Functionalized lanthanide coordination polymer nanoparticles for selective sensing of hydrogen peroxide in biological fluids

The fluorescence of Phe/Tb CPNPs functionalized with CPBA (Phe/Tb-CPBA CPNPs) was selectively quenched upon the addition of H₂O₂.

Functionalized silica nanoparticles: a platform for fluorescence imaging at the cell and small animal levels

Going in vivo, including living cells and the whole body, is very important for gaining a better understanding of the mystery of life and requires specialized imaging techniques. The diversity, composition, and temporal-spatial variation of life activities from cells to the whole body require the analysis techniques to be fast-response, noninvasive, highly sensitive, and stable, in situ and in real-time. Functionalized nanoparticle-based fluorescence imaging techniques have the potential to meet such needs through real-time and noninvasive visualization of biological events in vivo. Functionalized silica nanoparticles (SiNPs) doped with fluorescent dyes appear to be an ideal and flexible platform for developing fluorescence imaging techniques used in living cells and the whole body. We can select and incorporate different dyes inside the silica matrix either noncovalently or covalently. These form the functionalized hybrid SiNPs, which support multiplex labeling and ratiometric sensing in living systems. Since the silica matrix protects dyes from outside quenching and degrading factors, this enhances the photostability and biocompatibility of the SiNP-based probes. This makes them ideal for real-time and long-time tracking. One nanoparticle can encapsulate large numbers of dye molecules, which amplifies their optical signal and temporal-spatial resolution response. Integrating fluorescent dye-doped SiNPs with targeting ligands using various surface modification techniques can greatly improve selective recognition. Along with the endocytosis, functionalized SiNPs can be efficiently internalized into cells for noninvasive localization, assessment, and monitoring. These unique characteristics of functionalized SiNPs substantially support their applications in fluorescence imaging in vivo. In this Account, we summarize our efforts to develop functionalized dye-doped SiNPs for fluorescence imaging at the cell and small animal levels. We first discuss how to design and construct various functionalized dye-doped SiNPs. Then we describe their properties and imaging applications in cell surface receptor recognition, intracellular labeling, tracking, sensing, and controlled release. Additionally, we have demonstrated the promising application of dye-doped SiNPs as contrast imaging agents for in vivo fluorescence imaging in small animals. We expect these functionalized dye-doped SiNPs to open new opportunities for biological and medical research and applications.

Dual-emitting nanocomposites derived from rare-earth compound nanotubes for ratiometric fluorescence sensing applications

A new class of ratiometric fluorescence sensors composed of rare-earth (RE) compound nanotubes is described. Polyethylenimine-coated yttrium hydroxide fluoride nanotubes (YHF NTs) that were synthesized hydrothermally exhibit highly efficient fluorescence when doped with RE ions. The polyethylenimine on the NTs facilitates the incorporation of phosphors such as quantum dots or organic dyes onto the NT surface to produce dual-emitting nanocomposites which are excellent ratiometric fluorescence sensors. The phosphor layer and underlying tubes in the nanocomposites act as the indicator and reference probes, respectively. This ratiometric fluorescence method which can be applied to the detection of heavy metals in solutions, temperature sensing, and pH sensing boasts high sensitivity and selectivity as well as better accuracy than traditional intensity-based fluorescence methods.

An improved method for ratiometric fluorescence detection of pH and Cd2+ using fluorescein isothiocyanate-quantum dots conjugates

In this study, thioglycolic acid capped-CdTe quantum dots (QDs) were modified by polyethylenimine (PEI), and then combined with fluorescein isothiocyanate (FITC) to fabricate FITC-CdTe conjugates. The self-assembly of FITC, CdTe and PEI was ascribed to electrostatic interactions in aqueous solution. The resulting conjugates were developed toward two routes. In route one, ratiometric photoluminescence (PL) intensity of conjugates (IFITC/IQDs) was almost linear toward pH from 5.3 to 8.7, and a ratiometric PL sensor of pH was favorable obtained. In route two, firstly added S(2-) induced remarkable quenching of QDs PL peak (at the "OFF" state), which was restored due to following addition of Cd(2+) (at the "ON" state). In the conjugates, successive introduction of S(2-) and Cd(2+) hardly influenced on FITC PL peaks. According to this PL "OFF-ON" mode, a ratiometric PL method for the detection of Cd(2+) was achieved. Experimental results confirmed that the IFITC/IQDs exhibited near linear proportion toward Cd(2+) concentration in the range from 0.1 to 15μM, and the limit of detection was 12nM. Interferential experiments adequately testified that the proposed sensors of pH and Cd(2+) were practicable in real samples and complex systems. In comparison with conventional analytical techniques, the ratiometric PL method was simple, rapid, economic and highly selective.

Quantum dot-metallic nanorod sensors via exciton-plasmon interaction

We investigate quantum nanosensors based on hybrid systems consisting of semiconductor quantum dots and metallic nanorods in the near-infrared regime. These sensors can detect biological and chemical substances based on their impact on the coherent exciton-plasmon coupling and molecular resonances supported by such systems when they interact with a laser field. We demonstrate that the ultrahigh sensitivity of such molecular resonances on environmental conditions allows dramatic and nearly instantaneous changes in the total field experienced by the semiconductor quantum dot via minuscule variations of the local refractive indices of the quantum dot or nanorod. The proposed nanosensors can utilize quantum effects to control the sense (or direction) of the changes in the quantum dot emission, allowing us to have bistable switching from dark to bright states or vice versa via adsorption (or detachment) of biomolecules. These sensors can also offer detection of ultra-small variations in the local dielectric constant of the quantum dots or metallic nanorods via coherent induction of time delays in the effective field experienced by the quantum dots when the hybrid systems interact with time-dependent laser fields. This leads to unprecedented bulk refractive index sensitivities. Our results show that one can utilize quantum phase to control the coherent exciton-plasmon dynamics in these sensors such that introduction of a biomolecule can increase or decrease the time delay. These results offer novel ways to detect single biomolecules via application of quantum coherence to convert their impact into spectacular optical events.

Quantum dot based turn-on fluorescent probes for anion sensing

The design of fluorescent probes for turn-on sensing of anions has been especially significant because it can effectively enhance sensing sensitivity by decreasing the background interference. In the present work, we have systematically studied the potential applications of fluorescent quantum dots (QDs) in turn-on anion sensing. The fluorescence of QDs are firstly quenched by three different mechanisms, i.e. fluorescence resonance energy transfer, electron transfer and surface states modulated fluorescence. The fluorescence of the pre-quenched QDs can then be recovered by various anions due to the modulating effects of added anions on the interaction between QDs and QDs, the interaction between QDs and quenchers, and the surface chemistry of the quenched QDs, respectively. The results described here indicate that turn-on sensing of various anions by QDs-based systems can be achieved by rationally choosing fluorescence modulating strategies, demonstrating the versatility of QDs in the corresponding applications.