Fluorescence aggregation assay for the protein biomarker mucin 1 using carbon dot-labeled antibodies and aptamers

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Aptamer-Based Probes for Cancer Diagnostics and Treatment

Aptamers are single-stranded DNA or RNA oligomers that have the ability to generate unique and diverse tertiary structures that bind to cognate molecules with high specificity. In recent years, aptamer researches have witnessed a huge surge, owing to its unique properties, such as high specificity and binding affinity, low immunogenicity and toxicity, and simplicity of synthesis with negligible batch-to-batch variation. Aptamers may bind to targets, such as various cancer biomarkers, making them applicable for a wide range of cancer diagnosis and treatment. In cancer diagnostic applications, aptamers are used as molecular probes instead of antibodies. They have the potential to detect various cancer-associated biomarkers. For cancer therapeutic purposes, aptamers can serve as therapeutic or delivery agents. The chemical stabilization and modification strategies for aptamers may expand their serum half-life and shelf life. However, aptamer-based probes for cancer diagnosis and therapy still face several challenges for successful clinical translation. A deeper understanding of nucleic acid chemistry, tissue distribution, and pharmacokinetics is required in the development of aptamer-based probes. This review summarizes their application in cancer diagnostics and treatments based on different localization of target biomarkers, as well as current challenges and future prospects.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Next-Generation Intelligent MXene-Based Electrochemical Aptasensors for Point-of-Care Cancer Diagnostics

Delayed diagnosis of cancer using conventional diagnostic modalities needs to be addressed to reduce the mortality rate of cancer. Recently, 2D nanomaterial-enabled advanced biosensors have shown potential towards the early diagnosis of cancer. The high surface area, surface functional groups availability, and excellent electrical conductivity of MXene make it the 2D material of choice for the fabrication of advanced electrochemical biosensors for disease diagnostics. MXene-enabled electrochemical aptasensors have shown great promise for the detection of cancer biomarkers with a femtomolar limit of detection. Additionally, the stability, ease of synthesis, good reproducibility, and high specificity offered by MXene-enabled aptasensors hold promise to be the mainstream diagnostic approach. In this review, the design and fabrication of MXene-based electrochemical aptasensors for the detection of cancer biomarkers have been discussed. Besides, various synthetic processes and useful properties of MXenes which can be tuned and optimized easily and efficiently to fabricate sensitive biosensors have been elucidated. Further, futuristic sensing applications along with challenges will be deliberated herein.

Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Carbon dots (CDs) are a novel type of carbon-based nanomaterial that has gained considerable attention for their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence, which is attributed to a large number of organic functional groups (amino groups, hydroxyl, ketonic, ester, and carboxyl groups, etc.). In addition, they also demonstrate high stability and electron mobility. This article reviews the topic of doped CDs with organic and inorganic atoms and molecules. Such doping leads to their functionalization to obtain desired physical and chemical properties for biomedical applications. We have mainly highlighted modification techniques, including doping, polymer capping, surface functionalization, nanocomposite and core-shell structures, which are aimed at their applications to the biomedical field, such as bioimaging, bio-sensor applications, neuron tissue engineering, drug delivery and cancer therapy. Finally, we discuss the key challenges to be addressed, the future directions of research, and the possibilities of a complete hybrid format of CD-based materials.

Detection of β-Lactoglobulin by a Porous Silicon Microcavity Biosensor Based on the Angle Spectrum

In this paper, carbon quantum dot-labelled β-lactoglobulin antibodies were used for refractive index magnification, and β-lactoglobulin was detected by angle spectroscopy. In this method, the detection light is provided by a He-Ne laser whose central wavelength is the same as that of the porous silicon microcavity device, and the light source was changed to a parallel beam to illuminate the porous silicon microcavity’ surface by collimating beam expansion, and the reflected light was received on the porous silicon microcavity’ surface by a detector. The angle corresponding to the smallest luminous intensity before and after the onset of immune response was measured by a detector for different concentrations of β-lactoglobulin antigen and carbon quantum dot-labelled β-lactoglobulin antibodies, and the relationship between the variation in angle before and after the immune response was obtained for different concentrations of the β-lactoglobulin antigen. The results of the experiment present that the angle variations changed linearly with increasing β-lactoglobulin antigen concentration before and after the immune response. The limit of detection of β-lactoglobulin by this method was 0.73 μg/L, indicating that the method can be used to detect β-lactoglobulin quickly and conveniently at low cost.

Aptasensors versus immunosensors—Which will prevail?

Since the invention of the first biosensors 70 years ago, they have turned into valuable and versatile tools for various applications, ranging from disease diagnosis to environmental monitoring. Traditionally, antibodies have been employed as the capture probes in most biosensors, owing to their innate ability to bind their target with high affinity and specificity, and are still considered as the gold standard. Yet, the resulting immunosensors often suffer from considerable limitations, which are mainly ascribed to the antibody size, conjugation chemistry, stability, and costs. Over the past decade, aptamers have emerged as promising alternative capture probes presenting some advantages over existing constraints of immunosensors, as well as new biosensing concepts. Herein, we review the employment of antibodies and aptamers as capture probes in biosensing platforms, addressing the main aspects of biosensor design and mechanism. We also aim to compare both capture probe classes from theoretical and experimental perspectives. Yet, we highlight that such comparisons are not straightforward, and these two families of capture probes should not be necessarily perceived as competing but rather as complementary. We, thus, elaborate on their combined use in hybrid biosensing schemes benefiting from the advantages of each biorecognition element.

Detection of Hg2+ by a Dual-Fluorescence Ratio Probe Constructed with Rare-Earth-Element-Doped Cadmium Telluride Quantum Dots and Fluorescent Carbon Dots

Quantum dots (QDs) and carbon quantum dots (CDs) are classes of zero-dimensional materials whose sizes can be ≤10 nm. They exhibit excellent optical properties and are widely used to prepare fluorescent probes for qualitative and quantitative detection of test objects. In this article, we used cerium chloride as the cerium source and used the in situ doped cerium (rare-earth element) to develop cadmium telluride (CdTe) quantum dots following the aqueous phase method. CdTe: Ce quantum dots were successfully synthesized. The solution of CdTe:Ce QDs was mixed with the CD solution prepared following the green microwave method to form a ratio fluorescence sensor that can be potentially used for the selective detection of mercury ions (Hg²⁺). We used transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and other microscopy and spectral characterization techniques to validate that Ce had been successfully doped. The test results on the fluorescence performance revealed that Ce doping enhances the predoped fluorescence performance of the CdTe QDs. We have quantitatively detected Hg²⁺ using a ratiometric fluorescence sensor to show that in the range of 10-60 nM, the fluorescence quenching efficiency increases linearly with the increase in Hg²⁺ concentration. The linear correlation coefficient R ² = 0.9978, and its detection limit was found to be 2.63 nM L^-1. It was observed that other interfering ions do not significantly affect the fluorescence intensity of the probe. According to the results of the blank addition experiment, the developed proportional fluorescence probe can be used for the detection of Hg²⁺ in actual samples.

Aptamer-based fluorescent sensors for the detection of cancer biomarkers

Aptamers are short single-stranded RNA or DNA molecules that can recognize a series of targets with high affinity and specificity. Known as "chemical antibodies", aptamers have many unique merits, including ease of chemical synthesis, high chemical stability, low molecular weight, lack of immunogenicity, and ease of modification and manipulation compared to their protein counterparts. Using aptamers as the recognition groups, fluorescent aptasensors provide exciting opportunities for sensitive detection and quantification of analytes. Herein, we give an overview on the recent development of aptamer-based fluorescent sensors for the detection of cancer biomarkers. Based on various nanostructured sensor designs, we extended our discussions on sensitivity, specificity and the potential applications of aptamer-based fluorescent sensors in early diagnosis, treatment and prognosis of cancers.

Recent Developments of Carbon Dots in Biosensing: A Review

Early diagnosis of diseases is of great importance because it increases the chance of a cure and significantly reduces treatment costs. Thus, development of rapid, sensitive, and reliable biosensing techniques is essential for the benefits of human life and health. As such, various nanomaterials have been explored to improve performance of biosensors, among which, carbon dots (CDs) have received enormous attention due to their excellent performance. In this Review, the recent advancements of CD-based biosensors have been carefully summarized. First, biosensors are classified according to their sensing strategies, and the role of CDs in these sensors is elaborated in detail. Next, several typical CD-based biosensors (including CD-only, enzymatic, antigen-antibody, and nucleic acid biosensors) and their applications are fully discussed. Last, advantages, challenges, and perspectives on the future trends of CD-based biosensors are highlighted.

Recent advances in aptamer-based sensors for breast cancer diagnosis: special cases for nanomaterial-based VEGF, HER2, and MUC1 aptasensors

Cancer is one of the most common and important diseases with a high mortality rate. Breast cancer is among the three most common types of cancer in women, and the mortality rate has reached 0.024% in some countries. For early-stage preclinical diagnosis of breast cancer, sensitive and reliable tools are needed. Today, there are many types of biomarkers that have been identified for cancer diagnosis. A wide variety of detection strategies have also been developed for the detection of these biomarkers from serum or other body fluids at physiological concentrations. Aptamers are single-stranded DNA or RNA oligonucleotides and promising in the production of more sensitive and reliable biosensor platforms in combination with a wide range of nanomaterials. Conformational changes triggered by the target analyte have been successfully applied in fluorometric, colorimetric, plasmonic, and electrochemical-based detection strategies. This review article presents aptasensor approaches used in the detection of vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER2), and mucin-1 glycoprotein (MUC1) biomarkers, which are frequently studied in the diagnosis of breast cancer. The focus of this review article is on developments of the last decade for detecting these biomarkers using various sensitivity enhancement techniques and nanomaterials.

The application of antibody-aptamer hybrid biosensors in clinical diagnostics and environmental analysis

The growing number of various diseases and the increase of environmental contamination are the causes for the development of novel methods for their detection. The possibility of the application of affinity-based biosensors for such purposes seems particularly promising as they provide high selectivity and low detection limits. Recently, the usage of hybrid antibody-aptamer sandwich constructs was shown to be more advantageous in terms of working parameters in comparison to aptamer-based and immune-based biosensors. This review is focused on the usage of hybrid antibody-aptamer receptor layers for the determination of clinically and environmentally important target molecules. In this work, antibodies and aptamer molecules are characterized and the methods of their immobilization as well as analytical signal generation are shown. This is followed by the critical presentation of examples of hybrid sandwich biosensors that have been elaborated in the past 12 years.

Recent advancements in fabrication of nanomaterial based biosensors for diagnosis of ovarian cancer: a comprehensive review

Ovarian cancer is commonly diagnosed via determination of biomarkers like CA125, Mucin 1, HE4, and prostasin that can be present in the blood. However, there is a substantial need for less expensive, simpler, and portable diagnostic tools, both for timely diagnosis and management of ovarian cancer. This review (with 101 refs.) discusses various kinds of nanomaterial-based biosensors for tumor markers. Following an introduction into the field, a first section covers different kinds of biomarkers for ovarian cancer including CA125 (MUC16), mucin 1 (MUC1), human epididymis protein 4 (HE4), and prostasin. This is followed by a short overview on conventional diagnostic approaches. A large section is then presented on biosensors for determination of ovarian cancer, with subsections on optical biosensors (fluorimetric, colorimetric, surface plasmon resonance, chemiluminescence, electrochemiluminescence), on electrochemical sensors, molecularly imprinted sensors, paper-based biosensors, microfluidic (lab-on-a-chip) assays, chemiresistive and field effect transistor-based sensors, and giant magnetoresistive sensors. Tables are presented that give an overview on the wealth of methods and materials. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical abstract Schematic representation of the review covering the advancements in the fabrication of various nanomaterial based biosensors for diagnosis of ovarian cancer.

Electrochemical biosensors for the detection of lung cancer biomarkers: A review

Cancer is one of the most widespread challenges and important diseases, which has the highest mortality rate. Lung cancer is the most common type of cancer, so that about 25% of all cancer deaths are related to the lung cancer. The lung cancer is classified as two different types with different treatment methodology: the small cell lung carcinoma and nonsmall cell lung carcinoma are two categories of the lung cancer. Since the lung cancer is often in the latent period in its early stages, therefore, early diagnosis of lung cancer has many challenges. Hence, there is a need for sensitive and reliable tools for preclinical diagnosis of lung cancer. Therefore, many detection methods have been employed for early detection of lung cancer. As lung cancer tumors growth in the body, the cancerous cells release numerous DNA, proteins, and metabolites as special biomarkers of the lung cancer. The levels of these biomarkers show the stages of the lung cancer. Therefore, detection of the biomarkers can be used for screening and clinical diagnosis of the lung cancer. There are numerous biomarkers for the lung cancer such as EGFR, CEA, CYFRA 21-1, ENO1, NSE, CA 19-9, CA 125 and VEGF. Nowadays, electrochemical methods are very attractive and useful in the lung cancer detections. So, in this paper, the recent advances and improvements (2010-2018) in the electrochemical detection of the lung cancer biomarkers have been reviewed.

Aptamer-tagged silver nanoclusters for cell image and Mucin1 detection in vitro

Development of specific cell imaging technology for accurate tumor early diagnosis and evaluation of drug therapeutic efficiency is in great demand. In this study, a simple and sensitive fluorescence method for Mucin1 (MUC1) image in situ and quantitative assay in vitro has been established using APT-tagged silver nanoclusters (APT-Agnes) containing a recognition unit of MUC1 aptamer as the label-free fluorescence probe. The principle of the method is that specific recognition and binding of MUC1 with aptamer can result in the fluorescence quenching of APT-Agnes. The method for MUC1 assay showed a linear range from 0.1 to 100 NM with a limit of detection of 0.05 nM. Furthermore, the fluorescent probe of APT-AgNCs was successfully used for detection of MUC1 in serum and MCF-7 cell imaging. In our point, the above results demonstrated that the new simple method provided an alternative for direct quantitative assay of MUC1 in homogeneous solution and cell imaging, which is helpful for biomedical study and clinical diagnosis related with MUC1.

A fluorometric turn-on aptasensor for mucin 1 based on signal amplification via a hybridization chain reaction and the interaction between a luminescent ruthenium(II) complex and CdZnTeS quantum dots

A fluorometric method is described for the determination of the tumor biomarker mucin 1 (MUC1). It is based on signal amplification of the hybridization chain reaction (HCR), and the interaction between a luminescent ruthenium(II) complex and CdZnTeS quantum dots (QDs). If MUC1 bind to the biotin-labeled aptamer, it will initiate HCR with hairpins H₁ and H₂ to form a long-range dsDNA. The long nucleic acid chains are then linked on the surface of streptavidin-modified magnetic microparticles (MMPs) through streptavidin-biotin interaction. The luminescent ruthenium(II) complex is then embedded in the long dsDNA linked to the MMPs. Hence, there is little Ru complex in the supernatant after magnetic separation, and the fluorescence of the CdZnTeS QDs (best measured at excitation/emission wavelengths of 350/530 nm) is only slightly quenched. In the absence of target, the fluorescence of the CdZnTeS QDs is strongly quenched. Fluorescence increases linearly in the 0.2-100 ng·mL^-1 MUC1 concentration range, and the LOD is 0.13 ng·mL^-1 (at S/N = 3). The method was applied to the determination of MUC1 in spiked human serum samples. Graphical abstract A fluorometric turn-on aptasensor for mucin 1 is described that is based on the interaction between a Ru(II) complex and quantum dots (QDs). The detection system includes biotin-labeled aptamer-H₀, hairpins H₁ and H₂, streptavidin-modified magnetic microparticles (MMPs), Ru(bpy)₂(dppx)²⁺ and CdZnTeS QDs.

Carbon dots based immunosorbent assay for the determination of GFAP in human serum

Glial fibrillary acidic protein (GFAP) is expressed in the central nervous system and the level of GFAP normally rises with brain injury and astroglial tumors. So, serum GFAP is used as a marker for diagnosing various types of brain damage and astroglial tumors. In this study, a new sensor based on carbon dots (CDs) linked with antibodies to specifically detect GFAP in human serum was developed. Anti-GFAP (Ab1) linked with protein A/G agarose resin (PA/G) as a capture antibody (PA/G-Ab1) and anti-GFAP (Ab2) labeled with CDs as a detection antibody (CDs-Ab2) were prepared firstly. Then the CD-linked antibody immunosorbent assay (CLAISA) method was constructed based on the sandwich conjunction reaction among PA/G-Ab1, GFAP, and CDs-Ab2. CLAISA, using the fluorescence of PA/G-Ab1-GFAP-Ab2-CDs as the direct signal, enabled the proposed immunosensor to detect GFAP sensitively with a linear range of 0.10-8.00 ng ml^-1 and a detection limit of 25 pg ml^-1. This method was applied to the determination of GFAP in human serum by the standard addition method, and the results showed high accuracy and precision. Considering the easy synthetic process and excellent performance of CLAISA, this method has great potential to be used to monitor GFAP in the clinic.

A sensitive colorimetric aptasensor based on trivalent peroxidase-mimic DNAzyme and magnetic nanoparticles

In this study, a novel colorimetric aptasensor was prepared by coupling trivalent peroxidase-mimic DNAzyme and magnetic nanoparticles for highly sensitive and selective detection of target proteins. A three G-quadruplex (G4) DNA-hemin complex was employed as the trivalent peroxidase-mimic DNAzyme, in which hemin assisted the G4-DNA to fold into a catalytic conformation and act as an enzyme. The design of the aptasensor includes magnetic nanoparticles (MNPs), complementary DNA (cDNA) modified with biotin, and a label-free single strand DNA (ssDNA) including the aptamer and trivalent peroxidase-mimic DNAzyme. The trivalent DNAzyme, which has the highest catalytic activity among multivalent DNAzymes, catalyzed the H₂O₂-mediated oxidation of ABTS. The colorless ABTS was oxidized to produce a blue-green product that can be clearly distinguished by the naked eye. The aptamer and trivalent peroxidase-mimic DNAzyme promote the specificity and sensitivity of this detection method, which can be generalized for other targets by simply replacing the corresponding aptamers. To demonstrate the feasible use of the aptasensor for target detection, a well-known tumor biomarker MUC1 was evaluated as the model target. The limits of detection were determined to be 5.08 and 5.60 nM in a linear range of 50-1000 nM in a buffer solution and 10% serum system, respectively. This colorimetric and label-free aptasensor with excellent sensitivity and strong anti-interference ability has potential application in disease diagnoses, prognosis tracking, and therapeutic evaluation.

Phenylboronic Acid Templated Gold Nanoclusters for Mucin Detection Using a Smartphone-Based Device and Targeted Cancer Cell Theranostics

A phenylboronic acid templated gold nanocluster probe was developed to detect biomarker mucin by a noninvasive fluorescence-based method using a point-of-care smartphone-based fluorescence detection device. The gold nanocluster probe is able to detect mucin specifically. The same probe was applied for in vitro targeted bioimaging of HeLa and Hep G2 cancer cells, and it demonstrated specific therapeutic effects toward cancer cells as well as multicellular tumor spheroids imparting theranostic properties. The module is found to be more effective toward HeLa cells, and a pathway of cell death was established using flow-cytometry-based assays.

Ultrasensitive fluorescent aptasensor for MUC1 detection based on deoxyribonuclease I-aided target recycling signal amplification

A novel sensing strategy for sensitive detection of mucin 1 protein (MUC1) based on deoxyribonuclease I-aided target recycling signal amplification was proposed. In this paper, in the absence of MUC1, the MUC1 aptamer is absorbed on the surface of graphene oxide (GO) via π-stacking interactions. This results in quenching of the fluorescent label and no fluorescence signal is observed. Upon adding MUC1, the probe sequences could be specifically recognized by MUC1, leading to an increase in the fluorescence intensity. The detection limit is as low as 10 pg mL⁻¹, and a linear range from 50 pg mL⁻¹ to 100 ng mL⁻¹. The assay is specific and sensitive, and successfully applied to the determination of MUC1 in spiked human serum, urine and saliva. Importantly, the proposed aptasensing strategy has great potential in detecting various protein and even cancer cells.

A novel sensing strategy for sensitive detection of mucin 1 protein (MUC1) based on deoxyribonuclease I-aided target recycling signal amplification was proposed.

Carbon Dots-AS1411 Aptamer Nanoconjugate for Ultrasensitive Spectrofluorometric Detection of Cancer Cells

In the present study, a sensitive and selective signal-on method for aptamer based spectrofluorometric detection of cancer cells is introduced. AS1411, a nucleolin aptamer, is wrapped around water-soluble carbon dots and used as a probe for the detection of several types of cancer cells. Nucleolin, is overexpressed on the surface of cancer cells. Mouse breast 4T1, human breast MCF7, and human cervical HeLa cancer cells were selected as target cells, while human foreskin fibroblast cells HFFF-PI6 served as control cells. For the sensitive and selective spectrofluorimetric detection of target cancer cells in the presence of control cells, the cells were incubated in carbon dots-aptamer solutions, the cell suspensions were subsequently centrifuged and the fluorescence intensities were measured as an analytical signal. The specific targeting of cancer cells by AS1411 aptamers causes the release of carbon dots and enhances the fluorescence intensity. A calibration curve with a dynamic range between 10–4500 4T1 cells and detectability of roughly 7 cells was obtained. In addition, no significant change in the signal was detected by modifying the amount of human foreskin fibroblast control cells. Our results demonstrate similar responses to human MCF7 breast and cervical HeLa cancer cells.

Fluorometric immunoassay for human serum albumin based on its inhibitory effect on the immunoaggregation of quantum dots with silver nanoparticles

Quantitative determination of HSA was conducted by competitive immunoassay. Inhibition of aggregation of antibody conjugated quantum dots (QD) with albumin conjugated silver nanoparticles (AgNPs) in the presence of HSA was conducted. If antibody-loaded CdSe QDs aggregate with HSA-coated silver nanoparticles the distance between the two kinds of nanoparticles will be reduced enough to cause fluorescence resonance energy transfer (FRET). In this case the yellow fluorescence of the Ab-QDs is quenched. However if HSA (antigen) is added to the Ab-QDs their surface will be blocked and they cannot aggregate any longer with the HSA-AgNPs. Hence, fluorescence will not be quenched. The drop of the intensity of fluorescence (peaking at 570nm) is inversely correlated with the concentration of HSA in the sample. The method allows to determine HSA in the 30-600ng·mL^-1 concentration range.

Semiconductor and carbon-based fluorescent nanodots: the need for consistency

The need for establishing the bases and definitions of photoluminescent nanodots is discussed and their state-of-the-art in analytical and biomedical research fields is highlighted.