Protein–Conjugated Quantum Dots Interface: Binding Kinetics and Label-Free Lipid Detection

Nano-bio convergence unveiled: Systematic review on quantum dots-protein interaction, their implications, and applications

Quantum dots (QDs) are semiconductor nanocrystals (2-10 nm) with unique optical and electronic properties due to quantum confinement effects. They offer high photostability, narrow emission spectra, broad absorption spectrum, and high quantum yields, making them versatile in various applications. Due to their highly reactive surfaces, QDs can conjugate with biomolecules while being used, produced, or unintentionally released into the environment. This systematic review delves into intricate relationship between QDs and proteins, examining their interactions that influence their physicochemical properties, enzymatic activity, ligand binding affinity, and stability. The research utilized electronic databases like PubMed, WOS, and Proquest, along with manual reviews from 2013 to 2023 using relevant keywords, to identify suitable literature. After screening titles and abstracts, only articles meeting inclusion criteria were selected for full text readings. This systematic review of 395 articles identifies 125 articles meeting the inclusion criteria, categorized into five overarching themes, encompassing various mechanisms of QDs and proteins interactions, including adsorption to covalent binding, contingent on physicochemical properties of QDs. Through a meticulous analysis of existing literature, it unravels intricate nature of interaction, significant influence on nanomaterials and biological entities, and potential for synergistic applications harnessing both specific and nonspecific interactions across various fields.

Dye Degradation and Sulfur Oxidation of Methyl Orange and Thiophenol via Newly Designed Nanocomposite GQDs/NiSe-NiO Photocatalyst Under Homemade LED Light

Photocatalytic processes triggered by graphene-based photocatalysts under solar light have sparked interest as a new sort of instrument for solar chemical synthesis. Herein we investigated self-assembled graphene quantum dots (GQDs)/NiSe-NiO composite photocatalyst for organic transformation as well as dye degradation. The synthesized GQDs/NiSe-NiO composite photocatalyst has an excellent suitable band gap, high molar extinction coefficient, low toxicity and chemical/thermal stability. The GQDs/NiSe-NiO composite photocatalyst emerges as a new standard for sulfur oxidation and dye degradation reactions under homemade LED light with high yield.

Detection of Low Density Lipoprotein-Comparison of Electrochemical Immuno- and Aptasensor

An elevated level of low density lipoprotein (LDL) can lead to the cardiovascular system-related diseases, such as atherosclerosis and others. Therefore, fast, simple, and accurate methods for LDL detection are very desirable. In this work, the parameters characterizing the electrochemical immuno-and aptasensor for detection of LDL have been compared for the first time. An immunosensor has been designed, for which the anti-apolipoprotein B-100 antibody was covalently attached to 4-aminothiophenol (4-ATP) on the surface of the gold electrode. In the case of an aptasensor, the gold electrode was modified in a mixture of ssDNA aptamer specific for LDL modified with –SH group and 6-mercaptohexanol. Square-wave voltammetry has been used for detection of LDL in PBS containing redox active marker, [Fe(CN)₆]^3−/4−. Our results show the linear dependence of [Fe(CN)₆]^3−/4− redox signal changes on LDL concentration for both biosensors, in the range from 0.01 ng/mL to 1.0 ng/mL. The limit of detection was 0.31 and 0.25 ng/mL, for immuno- and aptasensor, respectively. Whereas slightly better selectivity toward human serum albumin (HSA), high density lipoprotein (HDL), and malondialdehyde modified low density lipoprotein (MDA-LDL) has been observed for aptasensor. Moreover, the other components of human blood serum samples did not influence aptasensor sensitivity.

Dual-modality microfluidic biosensor based on nanoengineered mesoporous graphene hydrogels

A dual-modality microfluidic biosensor is fabricated using a mesoporous nanostructured cysteine-graphene hydrogel for the quantification of human cardiac myoglobin (cMb). In this device, the nanoengineered mesoporous l-cysteine-graphene (Cys-RGO) hydrogel performs the role of a dual-modality sensing electrode for the measurements conducted using differential pulse voltammetry and surface plasmon resonance (SPR) techniques. High surface reactivity, mesoporous structure and fast electron transfer combined with good reaction kinetics of the graphene hydrogel in this device indicate excellent performance for the detection of human cardiac myoglobin in serum samples. In electrochemical modality, this microfluidic chip exhibits a high sensitivity of 196.66 μA ng^-1 mL cm^-2 for a linear range of concentrations (0.004-1000 ng mL^-1) with a low limit of detection (LOD) of 4 pg mL^-1 while the SPR technique shows a LOD of 10 pg mL^-1 for cMb monitoring in the range 0.01-1000 ng mL^-1. The intra-assay coefficient of variation was less than 8% for standard samples and 9% for real serum samples, respectively. This Cys-RGO hydrogel-based microfluidic SPR chip allows real-time dynamic tracking of cMb molecules with a high association constant of 4.93 ± 0.2 × 10⁵ M^-1 s^-1 and a dissociation constant of 1.37 ± 0.08 × 10^-4 s^-1, self-verification, reduced false readout, and improved detection reliability.

Advances in Molecularly Imprinting Technology for Bioanalytical Applications

In recent years, along with the rapid development of relevant biological fields, there has been a tremendous motivation to combine molecular imprinting technology (MIT) with biosensing. In this situation, bioprobes and biosensors based on molecularly imprinted polymers (MIPs) have emerged as a reliable candidate for a comprehensive range of applications, from biomolecule detection to drug tracking. Unlike their precursors such as classic immunosensors based on antibody binding and natural receptor elements, MIPs create complementary cavities with stronger binding affinity, while their intrinsic artificial polymers facilitate their use in harsh environments. The major objective of this work is to review recent MIP bioprobes and biosensors, especially those used for biomolecules and drugs. In this review, MIP bioprobes and biosensors are categorized by sensing method, including optical sensing, electrochemical sensing, gravimetric sensing and magnetic sensing, respectively. The working mechanism(s) of each sensing method are thoroughly discussed. Moreover, this work aims to present the cutting-edge structures and modifiers offering higher properties and performances, and clearly point out recent efforts dedicated to introduce multi-sensing and multi-functional MIP bioprobes and biosensors applicable to interdisciplinary fields.

Nanomaterial-based biosensors for measurement of lipids and lipoproteins towards point-of-care of cardiovascular disease

Cardiovascular disease (CVD) has become the primary cause of global deaths and inflicts an enormous healthcare burden on both developed and developing countries. Frequent monitoring of CVD-associated risk factors such as the level of lipids (e.g., triglyceride (TG) and total cholesterol (TC)) and lipoproteins (e.g., low-density lipoprotein (LDL) and high-density lipoprotein (HDL)) can effectively help prevent disease progression and improve clinical outcomes. However, measurement of these risk factors is generally integrated into an automated analyzer, which is prohibitively expensive and highly instrument-dependent for routine testing in primary care settings. As such, a variety of rapid, simple and portable nanomaterial-based biosensors have been developed for measuring the level of lipids (TG and TC) and lipoproteins (LDL and HDL) towards the management of CVD at the point-of-care (POC). In this review, we first summarize traditional methods for measurement of lipids and lipoproteins, and then present the latest advances in developing nanomaterial-based biosensors that can potentially monitor the risk factors of CVD at the POC.

A metal-free composite photocatalyst of graphene quantum dots deposited on red phosphorus

A simple approach to enhance the photocatalytic activity of red phosphorus (P) was developed. A mechanical ball milling method was applied to reduce the size of red P and to deposit graphene quantum dots onto red P. The product was characterized by scanning electron microscopy, transmission electron microscopy, contact angle measurements, zeta-potential measurements, X-ray diffraction and UV-vis absorption spectroscopy. The product exhibited high visible-light-driven photocatalytic performance in the photodegradation of rhodamine B.

Detection of Lipid and Amphiphilic Biomarkers for Disease Diagnostics

Rapid diagnosis is crucial to effectively treating any disease. Biological markers, or biomarkers, have been widely used to diagnose a variety of infectious and non-infectious diseases. The detection of biomarkers in patient samples can also provide valuable information regarding progression and prognosis. Interestingly, many such biomarkers are composed of lipids, and are amphiphilic in biochemistry, which leads them to be often sequestered by host carriers. Such sequestration enhances the difficulty of developing sensitive and accurate sensors for these targets. Many of the physiologically relevant molecules involved in pathogenesis and disease are indeed amphiphilic. This chemical property is likely essential for their biological function, but also makes them challenging to detect and quantify in vitro. In order to understand pathogenesis and disease progression while developing effective diagnostics, it is important to account for the biochemistry of lipid and amphiphilic biomarkers when creating novel techniques for the quantitative measurement of these targets. Here, we review techniques and methods used to detect lipid and amphiphilic biomarkers associated with disease, as well as their feasibility for use as diagnostic targets, highlighting the significance of their biochemical properties in the design and execution of laboratory and diagnostic strategies. The biochemistry of biological molecules is clearly relevant to their physiological function, and calling out the need for consideration of this feature in their study, and use as vaccine, diagnostic and therapeutic targets is the overarching motivation for this review.

Quantitative and multiplexed detection for blood typing based on quantum dot-magnetic bead assay

Background

Accurate and reliable blood grouping is essential for safe blood transfusion. However, conventional methods are qualitative and use only single-antigen detection. We overcame these limitations by developing a simple, quantitative, and multiplexed detection method for blood grouping using quantum dots (QDs) and magnetic beads.

Methods

In the QD fluorescence assay (QFA), blood group A and B antigens were quantified using QD labeling and magnetic beads, and the blood groups were identified according to the R value (the value was calculated with the fluorescence intensity from dual QD labeling) of A and B antigens. The optimized performance of QFA was established by blood typing 791 clinical samples.

Results

Quantitative and multiplexed detection for blood group antigens can be completed within 35 min with more than 10⁵ red blood cells. When conditions are optimized, the assay performance is satisfactory for weak samples. The coefficients of variation between and within days were less than 10% and the reproducibility was good. The ABO blood groups of 791 clinical samples were identified by QFA, and the accuracy obtained was 100% compared with the tube test. Receiver-operating characteristic curves revealed that the QFA has high sensitivity and specificity toward clinical samples, and the cutoff points of the R value of A and B antigens were 1.483 and 1.576, respectively.

Conclusion

In this study, we reported a novel quantitative and multiplexed method for the identification of ABO blood groups and presented an effective alternative for quantitative blood typing. This method can be used as an effective tool to improve blood typing and further guarantee clinical transfusion safety.

Microfluidic Immuno-Biochip for Detection of Breast Cancer Biomarkers Using Hierarchical Composite of Porous Graphene and Titanium Dioxide Nanofibers

We report on a label-free microfluidic immunosensor with femtomolar sensitivity and high selectivity for early detection of epidermal growth factor receptor 2 (EGFR2 or ErbB2) proteins. This sensor utilizes a uniquely structured immunoelectrode made of porous hierarchical graphene foam (GF) modified with electrospun carbon-doped titanium dioxide nanofibers (nTiO2) as an electrochemical working electrode. Due to excellent biocompatibility, intrinsic surface defects, high reaction kinetics, and good stability for proteins, anatase nTiO2 are ideal for electrochemical sensor applications. The three-dimensional and porous features of GF allow nTiO2 to penetrate and attach to the surface of the GF by physical adsorption. Combining GF with functional nTiO2 yields high charge transfer resistance, large surface area, and porous access to the sensing surface by the analyte, resulting in new possibilities for the development of electrochemical immunosensors. Here, the enabling of EDC-NHS chemistry covalently immobilized the antibody of ErbB2 (anti-ErbB2) on the GF-nTiO2 composite. To obtain a compact sensor architecture, the composite working electrode was designed to hang above the gold counter electrode in a microfluidic channel. The sensor underwent differential pulse voltammetry and electrochemical impedance spectroscopy to quantify breast cancer biomarkers. The two methods had high sensitivities of 0.585 μA μM(-1) cm(-2) and 43.7 kΩ μM(-1) cm(-2) in a wide concentration range of target ErbB2 antigen from 1 × 10(-15) M (1.0 fM) to 0.1 × 10(-6) M (0.1 μM) and from 1 × 10(-13) M (0.1 pM) to 0.1 × 10(-6) M (0.1 μM), respectively. Utilization of the specific recognition element, i.e., anti-ErbB2, results in high specificity, even in the presence of identical members of the EGFR family of receptor tyrosine kinases, such as ErbB3 and ErbB4. Many promising applications in the field of electrochemical detection of chemical and biological species will derive from the integration of the porous GF-nTiO2 composite into microfluidic devices.

Highly sensitive fluorescent determination of sulfide using BSA-capped CdS quantum dots

Schematic illustration of the BSA-CdS QD-based sensing system for sulfide detection.

A biofunctionalized quantum dot–nickel oxide nanorod based smart platform for lipid detection

A label-free and sensitive immunosensor has been fabricated using an antibody conjugated CdS–NiO nanocomposite for detection of lipids in serum samples.

Turn-off–on fluorescence probe based on 3-mercaptopropionic acid-capped CdS quantum dots for selective and sensitive lysozyme detection

The fluorescence of CdS QDs was first quenched by hemoglobin and then restored with the increasing concentration of the lysozyme in a certain range. Therefore, a fluorescence assay for the determination of lysozyme was established.

Tyrosinase conjugated reduced graphene oxide based biointerface for bisphenol A sensor

We have fabricated a nanocomposite of reduced graphene oxide (rGO) sheets and chitosan (Cn) polymer based highly sensitive electrochemical biosensor for detection of bisphenol A (BPA). The two-dimensional structure and chemical functionality of rGO and Cn provide an excellent electrode surface for loading of tyrosinase enzyme molecules. This rGO-Cn nanocomposite is capable of effectively utilizing their superior conductivity, larger effective surface area and superior electrochemical performance due to its synergistic effect between rGO and Cn. The structural, morphological and electrochemical characterizations of nanocomposite sheets have been performed by electron microscopy, X-ray diffraction, FTIR and Potentiostat/Galvanostat techniques. This fabricated biosensor is sensitive to nanomolar (0.74 nM) concentration of BPA and detection time is 10s compared to conventional BPA ELISA kit (0.3 µg/L and 2.5h). The rGO-Cn based biosensor exhibits a higher sensitivity (83.3 µA nM(-1) cm(-2)), wider linearity (0.01-50 µM) with good selectivity towards BPA. This biosensor is capable to quantify real sample of BPA using packaged drinking water bottles. This rGO-Cn nanocomposite sheets emerges as a potential electrode material for detection of other estrogenic substrate.

Evaluation of the interaction between naringenin and human serum albumin: Insights from fluorescence spectroscopy, electrochemical measurement and molecular docking

Naringenin (Nar) is a flavanone compound found in grapefruits that is endowed with diverse pharmacological and biological activities. Here, the interaction between Nar and human serum albumin (HSA) was investigated via various methods, including fluorescence spectroscopy, electrochemical methods and molecular docking. The Stern-Volmer quenching constants inversely correlated with temperature, demonstrating that the fluorescence quenching about HSA-Nar system is initiated by the formation of a compound, which has confirmed by electrochemical measurements. Three-dimensional fluorescence demonstrated that Nar induces the slight unfolding of the polypeptides of HSA. The calculated thermodynamic parameters suggesting that the binding of Nar to HSA is spontaneous, and the mainly force is electrostatic interactions. In addition, site marker competitive experiments indicated that Nar binds to HSA both on site I (subdomain IIA) and site II (subdomain IIIA), with higher affinity to the latter one, consistence with molecular docking. Furthermore, the fluorescence resonance energy transfer (FRET) experiment showed the binding distance (r) is 2.65 nm. And the effects of metal ions on the HSA-Nar system are also discussed.

Anti-epidermal growth factor receptor conjugated mesoporous zinc oxide nanofibers for breast cancer diagnostics

We report the fabrication of an efficient, label-free, selective and highly reproducible immunosensor with unprecedented sensitivity (femto-molar) to detect a breast cancer biomarker for early diagnostics. Mesoporous zinc oxide nanofibers (ZnOnFs) are synthesized by electrospinning technique with a fiber diameter in the range of 50-150 nm. Fragments of ZnOnFs are electrophoretically deposited on an indium tin oxide glass substrate and conjugated via covalent or electrostatic interactions with a biomarker (anti-ErbB2; epidermal growth factor receptor 2). Oxygen plasma treatment of the carbon doped ZnOnFs generates functional groups (-COOH, -OH, etc.) that are effective for the conjugation of anti-ErbB2. ZnOnFs without plasma treatment that conjugate via electrostatic interactions were also tested for comparison. Label-free detection of the breast cancer biomarker by this point-of-care device is achieved by an electrochemical impedance technique that has high sensitivity (7.76 kΩ μM(-1)) and can detect 1 fM (4.34 × 10(-5) ng mL(-1)) concentration. The excellent impedimetric response of this immunosensor provides a fast detection (128 s) in a wide detection test range (1.0 fM-0.5 μM). The oxy-plasma treated ZnOnF immunoelectrode shows a higher association constant (404.8 kM(-1) s(-1)) indicating a higher affinity towards the ErbB2 antigen compared to the untreated ZnOnF immunoelectrode (165.6 kM(-1) s(-1)). This sensor is about an order of magnitude more sensitive than the best demonstrated in the literature based on different nanomaterials and about three orders of magnitude better than the ELISA standard for breast cancer biomarker detection. This proposed point-of-care cancer diagnostic offers several advantages, such as higher stability, rapid monitoring, simplicity, cost-effectiveness, etc., and should prove to be useful for the detection of other bio- and cancer markers.

Protein functionalized carbon nanotubes-based smart lab-on-a-chip

A label-free impedimetric lab on a chip (iLOC) is fabricated using protein (bovine serum albumin) and antiapolipoprotein B functionalized carbon nanotubes-nickel oxide (CNT-NiO) nanocomposite for low-density lipoprotein (LDL) detection. The antiapolipoprotein B (AAB) functionalized CNT-NiO microfluidic electrode is assembled with polydimethylsiloxane rectangular microchannels (cross section: 100 × 100 μm). Cytotoxicity of the synthesized CNTs, NiO nanoparticles, and CNT-NiO nanocomposite has been investigated in the presence of lung epithelial cancer A549 cell line using MTT assay. The CNT-NiO nanocomposite shows higher cell viability at a concentration of 6.5 μg/mL compared to those using individual CNTs. The cell viability and proliferation studies reveal that the toxicity increases with increasing CNTs concentration. The X-ray photoelectron spectroscopy studies have been used to quantify the functional groups present on the CNT-NiO electrode surface before and after proteins functionalization. The binding kinetic and electrochemical activities of CNT-NiO based iLOC have been conducted using chronocoulometry and impedance spectroscopic techniques. This iLOC shows excellent sensitivity of 5.37 kΩ (mg/dL)(-1) and a low detection limit of 0.63 mg/dL in a wide concentration range (5-120 mg/dL) of LDL. The binding kinetics of antigen-antibody interaction of LDL molecules reveal a high association rate constant (8.13 M(-1) s(-1)). Thus, this smart nanocomposite (CNT-NiO) based iLOC has improved stability and reproducibility and has implications toward in vivo diagnostics.

Highly sensitive detection of 2,4,6-trinitrophenol (TNP) based on lysozyme capped CdS quantum dots

This work presents a novel method for nitroaromatic compound detection using lysozyme-capped CdS quantum dots (Lys-CdS QDs).

Peroxidase-mimicking DNAzyme modulated growth of CdS nanocrystalline structures in situ through redox reaction: application to development of genosensors and aptasensors

This work demonstrates the use of the peroxidase-mimicking DNAzyme (peroxidase-DNAzyme) as general and inexpensive platform for development of fluorogenic assays that do not require organic fluorophores. The system is based on the affinity interaction between the peroxidase-DNAzyme bearing hairpin sequence and the analyte (DNA or low molecular weight molecule), which changes the folding of the hairpin structure and consequently the activity of peroxidase-DNAzyme. Hence, in the presence of the analyte the peroxidase-DNAzyme structure is disrupted and does not catalyze the aerobic oxidation of l-cysteine to cystine. Thus, l-cysteine is not removed from the system and the fluorescence of the assay increases due to the in situ formation of fluorescent CdS nanocrystals. The capability of the system as a platform for fluorogenic assays was demonstrated through designing model geno- and aptasensor for the detection of a tumor marker DNA and a low molecular weight analyte, adenosine 5'triphosphate (ATP), respectively.

Lipid-lipid interactions in aminated reduced graphene oxide interface for biosensing application

A label-free biosensor based on antiapolipoprotein B 100 functionalized-aminated reduced graphene oxide interface has been fabricated for detection of low density lipoprotein (LDL or lipid) cholesterol. The aminated reduced graphene oxide (NH2-rGO) based electrode surface is covalently functionalized with antiapolipoprotein B 100 (AAB or lipid) using EDC/NHS coupling chemistry. The lipid-lipid interactions at the NH2-rGO electrode surface have been investigated using electrochemical impedance spectroscopic technique. The structural and morphological investigations of NH2-rGO based immunosensor have been accomplished via transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV-visible, and electrochemical techniques. The impedimetric response of the proposed immunosensor shows excellent sensitivity (612 Ω mg(-1) dL cm(-2)), a response time of 250 s, and a low detection limit of 5 mg/dL of LDL molecules. The association, dissociation, and equilibrium rate constants for this immunoelectrode are found to be 1.66 M(-1) s(-1), 0.6 s(-1), and 2.77 M(-1), respectively. The long-term stability and excellent reproducibility of the proposed immunosensor indicates a suitable platform for detection of LDL or lipid molecules. This immunosensor provides an efficient platform for analysis of the antigen-antibody interactions of lipid molecules.

An aptamer-based quartz crystal microbalance biosensor for sensitive and selective detection of leukemia cells using silver-enhanced gold nanoparticle label

An aptamer-based quartz crystal microbalance (QCM) biosensor was developed for the selective and sensitive detection of leukemia cells. In this strategy, aminophenylboronic acid-modified gold nanoparticles (APBA-AuNPs) which could bind to cell membrane were used for the labeling of cells followed by silver enhancement, through which significant signal amplification was achieved. Both the QCM and fluorescence microscopy results manifested the selectivity of the sensor designed. A good linear relationship between the frequency response and cell concentration over the range of 2×10(3)-1×10(5)cells/mL was obtained, with a detection limit of 1160cells/mL. This approach provides a simple, rapid, and economical method for leukemia cell analysis which might have great potential for further use.