Bifunctional magnetic nanoparticles for efficient cholesterol detection and elimination via host-guest chemistry in real samples

A hybrid catalyst-triggered cascade reaction for cholesterol detection using a smartphone-based miniature fluorescent apparatus

A new hybrid biological-chemical catalyst, magnetic nanoparticles functionalized with cholesterol oxidase (Fe3O4/APTES/ChOx), was developed for cholesterol detection. In the presence of cholesterol, the enzyme produced H2O2, which facilitated the generation of fluorescent molecules from the fluorogenic substrate with the assistance of Fe3O4 nanoparticles. A smartphone camera with a miniature fluorescent apparatus was used to assess fluorescence emission. Then, a smartphone application was employed to translate the fluorescence intensity to the red, green, and blue (RGB) domain. The developed approach achieved excellent selectivity and acceptable performances while supporting an onsite analysis approach. The practical operational range spanned from 5 to 100 nM, with a detection limit of 0.85 nM. Fe3O4/APTES/ChOx was applied for up to four replicates of reuse and demonstrated stability for at least 30 days. The applicability of the method was evaluated in milk samples, and the results were in accordance with the reference method.

Ultrasensitive electrochemical biosensors for dopamine and cholesterol: recent advances, challenges and strategies

The rapid and accurate determination of the dopamine (neurotransmitter) and cholesterol level in bio-fluids is significant because they are crucial bioanalytes for several lethal diseases, which require early diagnosis. The level of DA in the brain is modulated by the dopamine active transporter (DAT), and is influenced by cholesterol levels in the lipid membrane environment. Accordingly, electrochemical biosensors offer rapid and accurate detection and exhibit unique features such as low detection limits even with reduced volumes of analyte, affordability, simple handling, portability and versatility, making them appropriate to deal with augmented challenges in current clinical and point-of-care diagnostics for the determination of dopamine (DA) and cholesterol. This feature article focuses on the development of ultrasensitive electrochemical biosensors for the detection of cholesterol and DA for real-time and onsite applications that can detect targeted analytes with reduced volumes and sub-picomolar concentrations with quick response times. Furthermore, the development of ultrasensitive biosensors via cost-effective, simple fabrication procedures, displaying high sensitivity, selectivity, reliability and good stability is significant in the impending era of electrochemical biosensing. Herein, we emphasize on recent advanced nanomaterials used for the ultrasensitive detection of DA and cholesterol and discuss in depth their electrochemical activities towards ultrasensitive responses. Key points describing future perspectives and the challenges during detection with their probable solutions are discussed, and the current market is also surveyed. Further, a comprehensive review of the literature indicates that there is room for improvement in the miniaturization of cholesterol and dopamine biosensors for lab-on-chip devices and overcoming the current technical limitations to facilitate full utilization by patients at home.

Visual Quantitative Detection of Glutathione and Cholesterol in Human Blood Based on the Thiol-Ene Click Reaction-Triggered Wettability Change of the Interface

Herein, we proposed an innovative visual quantitative sensing strategy based on thiol-ene click chemistry and the capillary action principle. A triethoxyvinylsilane (VTEO)- or mercaptopropylsilatrane (MPS)-modified interface was prepared for analyte recognition. Target analyte molecules containing thiol groups or C═C double bonds are coupled to the VTEO- or MPS-modified inner surface of the glass capillary tube via a thiol-ene click reaction, respectively. Then, the molecular recognition events were transformed into the wettability change of the inner wall of the glass capillary. The concentration of the target molecules was quantified by reading the height change of the water column in the capillary tube. As a proof of concept, this strategy was successfully used to build visual quantitative sensors for detecting glutathione and cholesterol. In addition, this strategy showed a good anti-interference ability to complex biological fluids and realized sensitive glutathione (GSH) and cholesterol detection in real human blood samples.

Magnetic Nanoparticle-Based Ligand Replacement Strategy for Chemical Luminescence Determination of Cholesterol

Determination of serum cholesterol (Chol) is important for disease diagnosis, and has attracted great attention during the last few decades. Herein, a new magnetic nanoparticle-based ligand replacement strategy has been presented for chemical luminescence detection of Chol. The detection depends on ligand replacement from ferrocene (Fc) to Chol through a β-cyclodextrin (β-CD)-based host-guest interaction, which releases Fc-Hemin as a catalyst for the luminol/hydrogen peroxide chemical luminescence system. More importantly, the luminescence signal can be captured by the camera of a smartphone, thus realizing Chol detection with less instrument dependency. The limit of detection of this method is calculated to be 0.18 μM, which is comparable to some of the developed methods. Moreover, this method has been used successfully to quantify Chol from serum samples with a simple extraction process.

On-Site Colorimetric Detection of Cholesterol Based on Polypyrrole Nanoparticles

Herein, we report a facile method for cholesterol detection by coupling the peroxidase-like activity of polypyrrole nanoparticles (PPy NPs) and cholesterol oxidase (ChOx). ChOx can catalyze the oxidation of cholesterol to produce H₂O₂. Subsequently, PPy NPs, as a nanozyme, induce the reaction between H₂O₂ and 3,3',5,5'-tetramethylbenzidine (TMB). Under optimal conditions, the increase is proportional to cholesterol with concentrations from 10 to 800 μM in absorbance of TMB at 652 nm. The linear range for cholesterol is 10-100 μM, with a detection limit of 3.5 μM. This reported method is successfully employed for detection of cholesterol in human serum. The recovery percentage is ranged within 96-106.9%. Furthermore, we designed a facile and simple portable assay kit using the proposed system, realizing the on-site semiquantitative and visual detection of cholesterol in human serum. The cholesterol content detected from the portable assay kit were closely matching those obtained results from solution-based assays, thereby holding great potential in clinical diagnosis and health management.

Highly rapid and non-enzymatic detection of cholesterol based on carbon nitride quantum dots as fluorescent nanoprobes

In this work, we reported a highly rapid and non-enzymatic method for cholesterol measuring based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes, which were synthesized through chemical oxidation. The obtained CNQDs displayed high quantum yield up to 35% as well as excellent photostability, water solubility and low toxicity. We found that the fluorescence of CNQDs could be quenched more than 90% within 30 seconds by cholesterol through the formation of hydrogen bonds between –NH₂, –NH on the surface of CNQDs and cholesterol containing –OH. According to this phenomenon, a cholesterol detection method was constructed with a wide linear region over the range of 0–500 μmol L⁻¹ and a detection limit as low as 10.93 μmol L⁻¹, and it possessed the obvious advantages of being a very rapid process and avoiding the use of enzymes. In addition, this method showed high selectivity in the presence of various interfering reagents and applicability to the measurement of cholesterol in fetal bovine serum, which indicated its potential application value in clinical settings.

Highly rapid and non-enzymatic method for the detection of cholesterol was constructed based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes. The fluorescence of CNQDs could be effectively and rapidly quenched by cholesterol.

Click Reaction-Mediated T2 Immunosensor for Ultrasensitive Detection of Pesticide Residues via Brush-like Nanostructure-Triggered Coordination Chemistry

We develop an ultrasensitive T₂-mediated immunosensor based on the coordination chemistry and Cu(I)-catalyzed 1,3-dipolar cycloaddition of azide andalkyne (CuAAC) and apply it for the detection of pesticide residues. We functionalize polyglutamic acid (PGA) on polystyrene to form a brush-like nanostructure that has a large loading capacity of Cu(II) through the coordination chemistry between PGA and Cu(II). Such a brush-like nanostructure could be used to chelate Cu(II) to modulate the CuAAC between azide-functionalized 1000 nm polystyrene (PS₁₀₀₀) and alkyne-functionalized 30 nm magnetic nanoparticles (MNP₃₀), and the MNP₃₀-PS₁₀₀₀ conjugate as a product of CuAAC can act as a magnetic probe in this T₂-based immunosensor. This click chemistry and coordination chemistry-mediated immunosensor allows for an ultrasensitive detection for chlorpyrifos residue (0.022 ng/mL), a 58-fold enhancement compared with that of enzyme-linked immunosorbent assay (1.28 ng/mL), providing a promising platform for detection of trace small molecules.

Fabrication of polyethyleneimine-functionalized reduced graphene oxide-hemin-bovine serum albumin (PEI-rGO-hemin-BSA) nanocomposites as peroxidase mimetics for the detection of multiple metabolites

The ultrasensitive bioassays are increasingly demanded for disease diagnosis and environmental monitoring. The combined unique natures of the components in nanocomposites have led to their wide applications in bioanalysis. In the current study, a simple strategy for preparing polyethyleneimine-functionalized reduced graphene oxide-hemin-bovine serum albumin (PEI-rGO-Hemin-BSA) nanocomposites as peroxidase mimetics was demonstrated. The developed nanocomposites of PEI-rGO-Hemin-BSA showed an excellent peroxidase-like activity. Importantly, through the glutaradelhyde crosslinking, PEI-rGO-Hemin-BSA could be further simply combined with various oxidases such as glucose oxidase, cholesterol oxidase, lactate oxidase and choline oxidase for the detection and quantitative measurement of multiple metabolites including glucose, cholesterol, l-lactate, and choline. The developed detection strategy, which is sensitive, convenient, low-costed, and in tiny sample consumption, could be expected wide applications in the disease diagnosis and management of metabolite disorders.