Nanomaterial-based chemiluminescence resonance energy transfer: A strategy to develop new analytical methods

Recent Applications of Quantum Dots in Pharmaceutical Analysis

Nanotechnology has emerged as one of the most potential areas for pharmaceutical analysis. The need for nanomaterials in pharmaceutical analysis is comprehended in terms of economic challenges, health and safety concerns. Quantum dots (QDs)or colloidal semiconductor nanocrystals are new groups of fluorescent nanoparticles that bind nanotechnology to drug analysis. Because of their special physicochemical characteristics and small size, QDs are thought to be promising candidates for the electrical and luminescent probes development. They were originally developed as luminescent biological labels, but are now discovering new analytical chemistry applications, where their photo-luminescent properties are used in pharmaceutical, clinical analysis, food quality control and environmental monitoring. In this review, we discuss QDs regarding properties and advantages, advances in methods of synthesis and their recent applications in drug analysis in the recent last years.

A hybrid SERS sensing platform constructed by porous carbon/Ag nanoparticles for efficient imatinib detection in bio-environment

Surface enhanced Raman scattering (SERS) is a rapid and non-destructive spectral detection technique, and has been widely implemented on trace-level molecule detection. In this work, a hybrid SERS substrate constructed by porous carbon film and silver nanoparticles (PCs/Ag NPs) was developed and then used for imatinib (IMT) detection in bio-environment. The PCs/Ag NPs was prepared by direct carbonizing the gelatin-AgNO₃ film in the air atmosphere, and an enhancement factor (EF) of 10⁶ was achieved with R6G as the Raman reporter. Hereafter, this SERS substrate was used as the label-free sensing platform to detect the IMT in the serum, and the experimental results indicate that the substrate is conducive to eliminating the interference from the complex biological molecules in the serum, and the characteristic Raman peaks belonging to IMT (10^-4 M) are accurately resolved. Furthermore, the SERS substrate was used to trace the IMT in the whole blood, the trace of ultra-low concertation of IMT is rapidly discovered without any pretreatment. Thus, this work finally suggests that the proposed sensing platform provides a rapid and reliable method for IMT detection in the bio-environment and offers a potential for its application in therapeutic drug monitoring.

A chemiluminescent lantern: a coordination cage catalysed oxidation of luminol followed by chemiluminescence resonance energy-transfer

A molecule of luminol bound as guest inside a Co₈ coordination cage host undergoes oxidation by H₂O₂ to generate chemiluminescence by a process in which the Co(II) ions in the cage superstructure activate the H₂O₂: accordingly the cage not only co-locates the reactants but also acts as a redox partner in the catalysis. The luminescence from oxidation of the cavity-bound luminol can transfer its excitation energy to surface-bound fluorescein molecules in an unusual example of Chemiluminescence Resonance Energy Transfer (CRET).

Chemiluminescence in Combination with Organic Photosensitizers: Beyond the Light Penetration Depth Limit of Photodynamic Therapy

Photodynamic therapy (PDT) is a promising noninvasive medical technology that has been approved for the treatment of a variety of diseases, including bacterial and fungal infections, skin diseases, and several types of cancer. In recent decades, many photosensitizers have been developed and applied in PDT. However, PDT is still limited by light penetration depth, although many near-infrared photosensitizers have emerged. The chemiluminescence-mediated PDT (CL-PDT) system has recently received attention because it does not require an external light source to achieve targeted PDT. This review focuses on the rational design of organic CL-PDT systems. Specifically, PDT types, light wavelength, the chemiluminescence concept and principle, and the design of CL-PDT systems are introduced. Furthermore, chemiluminescent fraction examples, strategies for combining chemiluminescence with PDT, and current cellular and animal applications are highlighted. Finally, the current challenges and possible solutions to CL-PDT systems are discussed.

Detection of Alpha-Fetoprotein Using Aptamer-Based Sensors

Alpha-fetoprotein (AFP) is widely-known as the most commonly used protein biomarker for liver cancer diagnosis at the early stage. Therefore, developing the highly sensitive and reliable method of AFP detection is of essential demand for practical applications. Herein, two types of aptamer-based AFP detection methods, i.e., optical and electrochemical biosensors, are reviewed in detail. The optical biosensors include Raman spectroscopy, dual-polarization interferometry, resonance light-scattering, fluorescence, and chemiluminescence. The electrochemical biosensors include cyclic voltammetry, electrochemical impedance spectroscopy, and giant magnetic impedance. Looking into the future, methods for AFP detection that are high sensitivity, long-term stability, low cost, and operation convenience will continue to be developed.

Fluorescence Detection of Cancer Stem Cell Markers Using a Sensitive Nano-Aptamer Sensor

Antigen CD133 is a glycoprotein present on the surface of cancer stem cells (CSCs), which is a key molecule to regulate the fate of stem cells and a functional marker of stem cells. Herein, a novel fluorescence “turn-on” nano-aptamer sensor for quantifying CD133 was designed using hybridization between CD133-targeted aptamers and partially complementary paired RNA (ssRNA), which were modified on the surface of quantum dots (QDs) and gold nanoparticles (AuNPs), respectively. Owing to the hybridization of aptamers and ssRNA, the distance between QDs and AuNPs was shortened, which caused fluorescence resonance energy transfer (FRET) between them, and the florescence of QDs was quenched by AuNPs. When CD133 competitively replaced ssRNA and was bound to aptamers, AuNPs-ssRNA could be released, which led to a recovery of fluorescent signals of QDs. The increase in the relative value of fluorescence intensity was investigated to linearly correlate with the CD133 concentration in the range of 0–1.539 μM, and the detection limit was 6.99 nM. In confocal images of A549 cells, the CD133 aptamer sensor was further proved applicable in lung cancer cell samples with specificity, precision, and accuracy. Compared with complicated methods, this study provided a fresh approach to develop a highly sensitive and selective detection sensor for CSC markers.

State-of-the-art self-luminescence: a win–win situation

The working principles, luminescent mechanisms, versatile integrated approaches and advantages, and future perspectives of AIE-assisted “enhanced” self-luminescence systems are reviewed.

Synthesis of molecularly imprinted microspheres and development of a fluorescence method for detection of chloramphenicol in meat

In this study, nitrobenzene was used as dummy template to synthesize a type of specific molecularly imprinted microspheres for chloramphenicol, and 4-nitroaniline was coupled with three fluorophores to synthesize three fluorescent tracers. Then a competitive fluorescence method was developed on a conventional microplate for detection of chloramphenicol in chicken and pork samples. This method contained only one sample-loading step, so one assay was finished within 30 min. The IC₅₀ was 1.8 ng/ml, and the limit of detection was 0.06 ng/g. The recoveries from chloramphenicol-fortified blank meat samples were in the range 67.5-96.2%. Furthermore, this method could be recycled three times. The detection results for some real meat samples were identical to that of a LC-MS/MS method. Therefore, this method could be used as a practical tool for routine screening for the residue of chloramphenicol in large number of meat samples.

A sensitive immunosensor based on FRET between gold nanoparticles and InP/ZnS quantum dots for arginine kinase detection

Arginine kinase (AK) is one of the most important allergens in shrimp products. Herein, a novel immunoassay for quantitation of AK was developed using the antibody modified gold nanoparticle (AuNP) and quantum dot (QD). When the first antibody modified AuNP (AuNP-Ab1) was bridged by AK with the secondary antibody modified QD (QD-Ab2), fluorescence resonance energy transfer (FRET) would occur between the AuNP and QD, which led to a decrease in fluorescent signals. The decrease in fluorescence intensity was found to correlate linearly with the log of AK concentration in the range of 1.0 × 10^-6-1.0 × 10^-3 mg/mL (R² = 0.9909) and the detection limit was 0.11 ng/mL. The immunoassay was further proved to have encouraging specificity, precision and accuracy. Compared with existing methods, this study provided a promising approach to develop a highly sensitive and selective detection method for AK in shrimp related food samples.

Multicolor Chemiluminescent Resonance Energy-Transfer System for In Vivo High-Contrast and Targeted Imaging

Chemiluminescence (CL) resonance energy transfer (CRET) has received great attention due to its fascinating applications in in vivo imaging and photodynamic therapy. Here, we report a highly efficient CRET polymer dot (CRET-Pdots)-based system using catalytic CL reagents as energy donors and fluorescent polymers and dyes as energy acceptors. CRET-Pdots consist of Fe(III) deuteroporphyrin IX (CL catalyst), fluorescent polymers, and dyes. The CL intensity and duration are markedly enhanced by using ultrasensitive catalytic CL reaction of luminol analogue-H₂O₂, and the CL emission wavelength can be adjusted by one-step/two-step energy-transfer strategies. CRET-Pdots show intensive multicolor CL (about 3000× enhanced), an adjustable emission wavelength (470-720 nm), long CL duration (over 8 h), and a high CRET efficiency (50%). CRET-Pdots possess excellent biocompatibility, sensitive response to reactive oxygen species (ROS), and ultrahigh catalytic activity. They are successfully used for high-contrast real-time ROS imaging and in vivo tumor-targeted imaging with an excellent signal-to-noise ratio (over 90).

Antibody engineering-driven controllable chemiluminescence resonance energy transfer for immunoassay with tunable dynamic range

The donor-acceptor distance is a critical factor for the occurrence of chemiluminescent resonance energy transfer (CRET). We herein evaluate the donor-acceptor distance and transfer efficiency of CRET immunoassays of a series of donors which contain different sized antibody fragments, intact monoclonal antibody (IgG), antigen binding fragment (Fab), and single chain fragment antibody (scFv). Core/multishell quantum dots were used as the acceptor in three CRET systems. IgG is the maximum antibody fragment, leading to the longest donor-acceptor distance and the lowest transfer efficiency. Donors with Fab and scFv show significantly decreased distance and increased transfer efficiency. These results suggest an inverse correlation between donor size and transfer efficiency and can be used to provide guidance for the construction of controllable CRET. By combining the controllable CRET with immunoassay, we further develop a tunable sulfamethazine analytical system. Three different sized donors based CRET immunoassay show a markedly different sensitivity and dynamic range. Such adjustable detection provides greater flexibility for contaminant detection in different foodstuffs with different residue limits. This work not only illustrates the effect of donor-acceptor distance on regulating the energy transfer efficiency of CRET system, but also provides a guideline for the construction of a tunable immunoassay.

Chemiluminescence resonance energy transfer-based nanoparticles for quantum yield-enhanced cancer phototheranostics

Chemiluminescence (CL) has recently gained attention for CL resonance energy transfer (CRET)-mediated photodynamic therapy of cancer. However, the short duration of the CL signal and low quantum yield of the photosensitizer have limited its translational applications. Here, we report CRET-based nanoparticles (CRET-NPs) to achieve quantum yield-enhanced cancer phototheranostics by reinterpreting the hidden nature of CRET. Owing to reactive oxygen species (ROS)-responsive CO2 generation, CRET-NPs were capable of generating a strong and long-lasting photoacoustic signal in the tumor tissue via thermal expansion-induced vaporization. In addition, the CRET phenomenon of the NPs enhanced ROS quantum yield of photosensitizer through both electron transfer for an oxygen-independent type I photochemical reaction and self-illumination for an oxygen-dependent type II photochemical reaction. Consequently, owing to their high ROS quantum yield, CRET-NPs effectively inhibited tumor growth with complete tumor growth inhibition in 60% of cases, even with a single treatment.

Highly chemiluminescent TiO2/tetra(4-carboxyphenyl)porphyrin/N-(4-aminobutyl)-N-ethylisoluminol nanoluminophores for detection of heart disease biomarker copeptin based on chemiluminescence resonance energy transfer

In this work, the chemiluminescence (CL) property of 5,10,15,20-tetrakis(4-carboxyphenyl)-porphyrin- and N-(4-aminobutyl)-N-ethylisoluminol-functionalized TiO₂ nanoparticles (TiO₂-TCPP-ABEI nanoluminophores) was studied for the first time. It was found that TiO₂-TCPP-ABEI nanoluminophores exhibited excellent CL activity in the presence of H₂O₂. The CL mechanism has been proposed due to the reaction of ABEI with H₂O₂ and catalytic effect of TiO₂ and TCPP. Furthermore, trisodium citrate-stabilized gold nanoparticles were observed to effectively quench the CL of TiO₂-TCPP-ABEI due to CL resonance energy transfer (CRET). On this basis, a sensitive and selective CRET-based immunoassay was developed for the determination of copeptin by using TiO₂-TCPP-ABEI nanoluminophores as both CL nanointerface and energy donor, and using cit-AuNPs as an effective energy receptor. The immunoassay exhibited a wide dynamic range from 5 × 10^-12 to 1 × 10^-9 g mL^-1 with a low detection limit of 1.54 × 10^-12 g mL^-1, which was superior to previously reported CL-based immunoassays. It was successfully applied for the determination of copeptin in serum samples, which would provide a good practical perspective on the clinical diagnosis. This strategy may also be used for the detection of other antigens if corresponding antibodies are available. Graphical abstract.

Detection of chloramphenicol in meat with a chemiluminescence resonance energy transfer platform based on molecularly imprinted graphene

In this study, a novel composite was synthesized by polymerizing the dummy-template molecularly imprinted microspheres on the surface of magnetic graphene. This composite was used as recognition reagent and energy acceptor to develop a platform for determination of chloramphenicol according to the principle of chemiluminescence resonance energy transfer. The light signal was induced with luminolH₂O₂4-(imidazole-1-yl)phenol system, and the chemiluminescence intensity was positively correlated with the analyte concentration. The limit of detection for chloramphenicol in meat sample was 2.0 pg/g, and the recoveries from the standard fortified blank meat sample were in the range of 69.5%-97.3%. Furthermore, one single assay could be finished within 10 min, and the magnetic composite could be reused for at least thirty times. Therefore, this platform could be used as a rapid, simple, sensitive, accurate and recyclable tool for screening the residue of chloramphenicol in meat.

An fluorescent aptasensor for sensitive detection of tumor marker based on the FRET of a sandwich structured QDs-AFP-AuNPs

The detection of alpha-fetoprotein (AFP) is of great importance for hepatocellular carcinoma (HCC) diagnosis, but it needs to be further improved because of poor sensitivity and complicated operating steps. In this paper, a simple and sensitive homogeneous apatasensor for AFP has been developed based on Förster resonance energy transfer (FRET) where the AFP aptamer labeled luminescent CdTe quantum dots (QDs) as a donor and anti-AFP antibody functional gold nanoparticles (AuNPs) as an acceptor. In the presence of AFP, the bio-affinity between aptamer, target, and antibody made the QDs and AuNPs close enough, thus the fluorescence of CdTe QDs quenched though the FRET between QD and AuNP. The fluorescent aptasensor for AFP showed a concentration-dependent decrease of fluorescence intensity in the low nanomolar range and a detecting linear range of 0.5-45 ng mL^-1, with a detection limit of 400 pg mL^-1. Moreover, this homogeneous aptasensor is simple and reliable, and obtained satisfying results for the detection of AFP in human serum samples. With more and more aptamers for biomarkers have been selected gradually, this approach could be easily extended to detection of a wide range of biomarkers. The proposed aptasensor has great potential for carcinoma screening in point-of-care testing and even in field use.

Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System

Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH₂) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (K_SV ~ 10⁸-10¹⁰ M^-1) was calculated to be ca. 10⁴ times more for surface quoted NPs in comparison with BSA-NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH₂ captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs. Graphical Abstract Energy transfer from excited luminol to metal nanoparticles is strongly modulated in presence of serum albumins.

A turn-on chemiluminescence biosensor for selective and sensitive detection of adenosine based on HKUST-1 and QDs-luminol-aptamer conjugates

In this work, HKUST-1 and QDs-luminol-aptamer conjugates were prepared. The QDs-luminol-aptamer conjugates can be adsorbed by graphene oxide through π-π conjugation. When the adenosine was added, the QDs-luminol-aptamer conjugates were released from magnetic graphene oxide (MGO), the chemiluminescent switch was turned on. It was reported that HKUST-1 can catalyze the chemiluminescence reaction of luminol-H₂O₂ system in an alkaline medium, and improve the chemiluminescence resonance energy transfer (CRET) between chemiluminescence and QDs indirectly. Thus, the adenosine can be detected sensitively. Based on this phenomenon, the excellent platform for detection of adenosine was established. Under the optimized conditions, the linear detection range for adenosine was 1.0 × 10^-12-2.2 × 10^-10 mol/L with a detection limit of 2.1 × 10^-13 mol/L. The proposed method was successfully used for adenosine detection in biological samples.

A chemiluminescence resonance energy transfer for the determination of indolyl acetic acid using luminescent nitrogen-doped carbon dots as acceptors

A CRET method was fabricated for the determination of IAA using Ce(iv)–Na₂SO₃ as the donor and N-CDs as the acceptor.

Recent advances and developments on integrating nanotechnology with chemiluminescence assays

Chemiluminescence (CL) techniques are extensively utilized for detection of analytes due to their high sensitivity, rapidity and selectivity. With the advent of nanotechnology and incorporation of the nanoparticles in the CL system has revolutionized the assays due to their unique optical and mechanical properties. Several CL-based reactions have been developed where these nanoparticle based CL sensors have evolved as excellent prospects for sensing in various analytical applications. This review article addresses the nanoparticles based CL detection system that are recently developed, the mechanisms has been summarized and the role of luminophors have been discussed. This article critically analyzes the optimal conditions for the CL detection along with quantitative assessment of the analytes. We have included the use of semiconductor nanoparticles, metal nanoparticles, graphene based nanostructures, mesoporous nanospheres, layered double hydroxides, clays for CL detection. The scope and application of these nanoscale material based CL system in various branches of science and technology including chemistry, biomedical applications, pharmaceutics, food, environmental and toxicological applications has been critically summarized.

Determination of dihydralazine based on chemiluminescence resonance energy transfer of hollow carbon nanodots

The famous weak chemiluminescence (CL) system of potassium permanganate and sodium bisulfite (KMnO₄-HSO₃^-) was enhanced by the hollow fluorescent carbon nanodots (HCNs). The investigation of mechanism revealed that the enhanced CL was induced by the excited-state HCNs (HCNs^⁎), which could be produced from the electron-transfer annihilation of positively charged HCNs (HCNs⁺) and negatively charged HCNs (HCNs^-) as well as by CL resonance energy transfer (CRET) from excited SO₂ (SO₂^⁎)/¹O₂ to HCNs. The dihydralazine sulfate (DHZS) had a diminishing effect on the CL of HCNs-KMnO₄-HSO₃^- system due to the competitive consumption of O₂^-. Under the optimal conditions, the reduced CL signal with the concentration of DHZS was linear in the range of 1.0×10^-7-7.0×10^-5mol/L with a detection limit of 3.0×10^-8mol/L. The relative standard deviation for seven repeated determination of 5.0×10^-6mol/L DHZS was 2.1%. The established method was applied to the determination of DHZS in pharmaceutical preparations, human urine and plasma samples with good precision and accuracy.

Recent advances in chemiluminescence based on carbonaceous dots

Herein, a broad overview concerning the most recent progress of carbon dots (CDs) in chemiluminescence (CL) as well as the mechanisms and applications are presented. CDs have excellent optical and electronic properties and are very important advancement in the fast growing domain of nanotechnology. CDs enhance the ultraweak CL of different systems. The mechanisms and applications of these enhanced CL reactions are discussed. It is worthy to note that CDs participate in CL reactions as catalysts, energy acceptors or are directly involved in redox reactions with radicals in CL systems. Sometimes, these processes taking place simultaneously to enhance CL intensity. In this report, recent advances in CD based CL are comprehensively summarized and their applications in detection of various reagents and biological molecules are reviewed. The challenges and future prospects of this field are also discussed.

Chemiluminescence Resonance Energy Transfer Competitive Immunoassay Employing Hapten-Functionalized Quantum Dots for the Detection of Sulfamethazine

We describe a new strategy for using chemiluminescence resonance energy transfer (CRET) by employing hapten-functionalized quantum dots (QDs) in a competitive immunoassay for detection of sulfamethazine (SMZ). Core/multishell QDs were synthesized and modified with phospholipid-PEG. The modified QDs were functionalized with the hapten 4-(4-aminophenyl-sulfonamido)butanoic acid. The CRET-based immunoassay exhibited a limit of detection for SMZ of 9 pg mL(-1), which is >4 orders of magnitude better than a homogeneous fluorescence polarization immunoassay and is 2 orders of magnitude better than a heterogeneous enzyme-linked immunosorbent assay. This strategy represents a simple, reliable, and universal approach for detection of chemical contaminants.

In Situ Generation and Consumption of H2O2 by Bienzyme-Quantum Dots Bioconjugates for Improved Chemiluminescence Resonance Energy Transfer

Exploration of quantum dots (QDs) as energy acceptors revolutionizes the current chemiluminescence resonance energy transfer (CRET), since QDs possess large Stokes shifts and high luminescence efficiency. However, the strong and high concentration of oxidant (typically H2O2) needed for luminol chemiluminescence (CL) reaction could cause oxidative quenching to QDs, thereby decreasing the CRET performance. Here we proposed the use of bienzyme-QDs bioconjugate as the energy acceptor for improved CRET sensing. Two enzymes, one for H2O2 generation (oxidase) and another for H2O2 consumption (horseradish peroxidase, HRP), were bioconjugated onto the surface of QDs. The bienzyme allowed fast in situ cascaded H2O2 generation and consumption, thus alleviating fluorescence quenching of QDs. The nanosized QDs accommodate the two enzymes in a nanometric range, and the CL reaction was confined on the surface of QDs accordingly, thereby amplifying the CL reaction rate and improving CRET efficiency. As a result, CRET efficiency of 30-38% was obtained; the highest CRET efficiency by far was obtained using QDs as the energy acceptor. The proposed CRET system could be explored for ultrasensitive sensing of various oxidase substrates (here exemplified with cholesterol, glucose, and benzylamine), allowing for quantitative measurement of a spectrum of metabolites with high sensitivity and specificity. Limits of detection (LOD, 3σ) for cholesterol, glucose, and benzylamine were found to be 0.8, 3.4, and 10 nM, respectively. Furthermore, multiparametric blood analysis (glucose and cholesterol) is demonstrated.

A review on fluorescent inorganic nanoparticles for optical sensing applications

Fluorescent inorganic nanoparticles are immerging novel materials that can be adopted for a large number of optical bioassays and chemical sensing probes.