Emerging trends in the cystatin C sensing technologies: towards better chronic kidney disease management

Cystatin C (CysC), a protein, has replaced creatinine as a biomarker of kidney function and other diseases and has led to a surge in the research on the development of efficient CysC biosensors. The current CysC sensing technologies are remarkable in terms of selectivity and reproducibility. However, the complexity, cost, and space requirements of these methods render them unsuitable for real-time monitoring or point-of-care (PoC) implementations in healthcare settings. This review discusses the most recent developments in the field of CysC biosensing and to the best of our knowledge, this is the first focused review exclusively on CysC biosensing modalities. Our goal is to provide a thorough overview of the current state of CysC biosensors, and presenting mechanisms related to biosensor recognition and transduction. The review starts with clinical significance of CysC detection followed by detailed analysis of different CysC biosensing methods with emphasis on the necessity of PoC monitoring of CysC. We have also highlighted current challenges and an outlook on future perspectives. We anticipate that this study will play a key role in the understanding the working principle of CysC sensors and will aid in the designing of new efficient sensing modalities for the detection of CysC.

FRET-Based Dual-Color Carbon Dot Ratiometric Fluorescent Sensor Enables the Smartphone-Integrated Device for Noninvasive and Portable Diagnosis of Chronic Kidney Disease

Cystatin C (Cys C), a crucial renal disease marker for chronic kidney disease (CKD), plays a vital role in early diagnosis and treatment guidance. However, most current methods for detecting Cys C rely on a single signal and find it difficult to perform noninvasive and portable diagnosis. Here, we developed a ratiometric fluorescent carbon dot (CD) detection system for point-of-care testing (POCT) of Cys C through fluorescence resonance energy transfer (FRET). The detection is based on the hydrolysis effect of papain on a bovine serum albumin (BSA) scaffold and the specific inhibitory effect of Cys C on papain, endowing high-resolution color variance. Moreover, a low-cost, portable, yet reliable smartphone-assisted miniaturized device for real-time quantitative POCT of Cys C has been developed with a limit of detection (LOD) as low as 0.4 μg/mL. This sensing platform can effectively differentiate patients from healthy volunteers, which facilitates self-screening for healthy individuals and home monitoring for CKD patients.

Advances in Biosensor Technologies for Acute Kidney Injury

Acute kidney injury (AKI) is one of the most prevalent and complex clinical syndromes with high morbidity and mortality. The traditional diagnosis parameters are insufficient regarding specificity and sensitivity, and therefore, novel biomarkers and their facile and rapid applications are being sought to improve the diagnostic procedures. The biosensors, which are employed on the basis of electrochemistry, plasmonics, molecular probes, and nanoparticles, are the prominent ways of developing point-of-care devices, along with the mutual integration of efficient surface chemistry strategies. In this manner, biosensing platforms hold pivotal significance in detecting and quantifying novel AKI biomarkers to improve diagnostic interventions, potentially accelerating clinical management to control the injury in a timely manner. In this review, novel diagnostic platforms and their manufacturing processes are presented comprehensively. Furthermore, strategies to boost their effectiveness are also indicated with several applications. To maximize these efforts, we also review various biosensing approaches with a number of biorecognition elements (e.g., antibodies, aptamers, and molecular imprinting molecules), as well as benchmark their features such as robustness, stability, and specificity of these platforms.

Development and Evaluation of Europium-Based Quantitative Lateral Flow Immunoassay for the Chronic Kidney Disease Marker Cystatin-C

This study aimed to establish a Europium label time-resolved fluorescence immunoassay (TRFIA) to detect the chronic kidney disease (CKD) biomarker Cystatin-C. An Europium based Time resolved fluorescence immunoassay was developed to detect the concentration of Cystatin-C in a urine sample to increase the sensitivity with captured anti-Cystatin-C antibodies immobilized on nitrocellulose membrane and then bonded with detection anti-Cystatin-C labelled with CM-EU, followed by fluorescence measurement using time-resolved fluorometry in 15 min. The performance of this TRFIA was evaluated using the clinical urine serum and compared with the ELISA assays. The linear calibration range was 0.015-32 µg/ml, and the limit of detection (LOD) quantified was 0.0001 µg/ml. This current work has improved the LOD of our previous work from 0.013 µg/ml to 0.001 µg/ml. These results indicated that the CM-EU nanoparticle-based LFIA is rapid, more sensitive, reliable, and reproducible for point-of-care testing of Cys-C concentrations in urine.

Developing a novel and simple biosensor for Cystatin C as a fascinating marker of glomerular filtration rate with DNase I-aided recycling amplification strategy

Cystatin C (Cys C) has been proposed as a fascinating glomerular filtration rate (GFR) marker for early detection of acute kidney injury and chronic kidney disease. However, most of traditional methods for Cys C detection are immunoassays, which was tedious to perform and unfriendly for economics. In this work, a novel and simple biosensor for the sensitive measurement of Cys C via DNase I-aided recycling amplification strategy was successfully constructed based on the graphene oxide (GO) and fluorophore-labelled aptamer, which can be used to the early prediction of kidney injury. The fluorescence of fluorophore-labelled aptamer was quenched by GO based on the Fluorescence Resonance Energy Transfer (FRET) and recovered with the existence of Cys C. In addition, the DNase I enzyme would digest the fluorophore-labelled aptamer and dissociate the Cys C to launch the next reaction, resulting in an increase of signal amplification. Hence, the limit of detection is found to be 0.16 ng mL^-1, which is almost 3 times lower than that without DNase I. Consequently, the developed biosensor offers a novel approach towards simple and rapid detection of Cys C based on the integration of GO and aptamer. Conceivably, this strategy holds a wide scope in the application of numerous other analytes if corresponding aptamers are available.

Development and Evaluation of a Quantitative Fluorescent Lateral Flow Immunoassay for Cystatin-C, a Renal Dysfunction Biomarker

The diagnosis, prognosis, and control of chronic kidney disease rely on an understanding of the glomerular filtration rate (GFR). The renal clearance of the cystatin-C is closely associated with the GFR. Cystatin-C is a more suitable GFR marker than the commonly used creatinine. General techniques for cystatin-C calculation, such as particle-enhanced turbidimetric and nephelometric assay, are time-consuming and tedious. Here, we propose a rapid, quantitative immunoassay for the detection of cystatin-C. A fluorescence-based lateral-flow kit was developed in a sandwich format by using a monoclonal antibody. A Linear calibration was obtained over the clinical diagnostic range of 0.023-32 µg/mL and the limit of detection (LOD) was 0.023 µg/mL and the limit of quantification (LOQ) was 0.029 µg/mL. Average recoveries from spiked urine samples ranged from 96-100% and the coefficient of variation was less than 4% for both intra and inter-day assays with excellent repeatability. With the comparison with an ELISA kit, the developed kit is highly sensitive, performs well over the detection range, provides repeatable results in a short time, and can easily be used at point-of-care (POC), making it an ideal candidate for rapid testing in early detection, community screening for renal function disorders.

Hierarchical Plasmonic-Fluorescent Labels for Highly Sensitive Lateral Flow Immunoassay with Flexible Dual-Modal Switching

Lateral flow immunoassay (LFIA), as a prominent point-of-care (POC) test platform, has been extensively adopted for rapid, on-site, and facile diagnosis of pathogen infections and disease biomarkers. Exploring novel structured optical labels of LFIA with amplified signal and complementary detection modes favors the sensitive and flexible POC diagnosis. Here, bimodal labels with both colorimetric and fluorescent readout were fabricated via a layered sequential assembly strategy based on affinity templates and hydrophobic metal-containing nanounits. High-quality colorimetric and fluorescent nanoparticles were densely incorporated into the colloidal supports and confined in separated regions, without interfering with each other. The hierarchical integration of gold nanoparticles and quantum dots with high loading density and good optical preservation realized dual readout and amplified signals from the assemblies of individual single nanoparticles. The "all-in-one" optical labels allowed both colorimetric and fluorescent detection of cystatin C (Cys C) after surface conjugation with antibodies. The LFIA strips revealed noninterfering dual signals for both visual inspection and quantitative detection of Cys C via the naked eye and portable devices, respectively. The limits of detection by colorimetric and fluorescent modes were 0.61 and 0.24 ng mL^-1, respectively. The novel LFIA platform demonstrated sensitive, specific, and reproducible POC testing of biomarkers with flexible detection modes and was reliable for clinical diagnosis.

An ultrasensitive Cystatin C renal failure immunosensor based on a PPy/CNT electrochemical capacitor grafted on interdigitated electrode

An interdigitated immunosensor for Cystatin C detection based on polypyrrole/carbon nanotube electrochemical capacitor is described. Cystatin C (CysC) is powerful biomarker for early acute renal failure and one predictive for cardiovascular risk, sepsis, cancer and death. Recently, electrochemical immunosensors based on interdigitated electrodes (IDE) have been successfully focused on development of point-of-care testing, due to their miniaturization facilities and higher sensitivity as compared with the screen-printed electrochemical sensing. Herein, a polypyrrole/carbon nanotube nanoyhibrid film was grafted on two gold fingers by electropolymerization obtaining a supercapacitor. Anti-CysC antibodies were immobilized on the IDE by covalent entrapment via ethylenediamine bifunctional agent, followed by glycine blocking in acid and alkaline medium. Under low frequency, capacitive effect of antigen-antibody interaction were observed by double layer capacitance, and analytical responses of this IDE immunosensor to CysC serum were obtained by changes on phase angle a linear range up to 300 ng/mL. The cutoff was calculated for serum samples showing a total reducing of non-specific binding at approximately 28 ng/mL CysC. This immunosensor based on interdigitated electrode (IDE) is a potential tools as portable device,with possibility to use as a practical and rapid test for CysC diagnostic in samples of serum.

Disposable electrochemical immunosensor for analysis of cystatin C, a CKD biomarker

Specific monitoring of cystatin C (CysC) levels in biological fluids is critical for diagnosis, treatment and mechanistic understanding of a spectrum of diseases, particularly chronic kidney disease (CKD). Despite evidences that CysC correlates with the high risk and/or progression of CKD, its use in clinical practice is still scarce. In this context, we report the development of a simple and sensitive immunosensor for the detection of CysC. The biosensor combines the technology of cost-effective screen-printed electrodes with the high specificity of a sandwich immunoassay. Optimized conditions showed that the sensor operates in a linear range between 10 and 100 ng mL^-1, with a detection limit and a sensitivity of 6.0 ng mL^-1 and 6.4 ± 0.3 μA ng mL^-1 cm^-2, respectively. Moreover, the sensor provided precise results (RSD ≤ 6.2%) and the quantification of CysC in CKD serum samples revealed to be in agreement with the values obtained by a particle-enhanced nephelometric immunoassay. In this light, the proposed immunosensor qualifies for clinical application, constituting a step forward in the development of fast, sensitive and cost-effective diagnostic tools that can improve the current medical care settings of CKD patients.

A dual-emission nano-rod MOF equipped with carbon dots for visual detection of doxycycline and sensitive sensing of MnO4. RSC Adv 2018;8:4766-4772. [PMID: 35539556 PMCID: PMC9077844 DOI: 10.1039/c7ra12252g]

Herein, ethanediamine-modified carbon dots (CDs) were encapsulated into luminescent MOF(Eu), which was designed for a dual-emission hybrid material (CDs@MOF(Eu)) with diverse fluorescence applications. This material exhibited high selectivity and sensitivity towards doxycycline. With an increasing concentration of doxycycline, the blue light emission of CDs could be quenched, whereas the red light emission of MOF(Eu) was enhanced. In view of this result, more convenient "test paper" was used first as a new tool for doxycycline detection, the colour of which turned from blue-purple to red as observed by the naked eyes under 365 nm UV-irradiation. This hybrid material also was a probe for sensing MnO4 - with a low limit of detection and good anti-interference performance. We propose that CDs can improve detection sensitivity compared with the original MOF(Eu). The possible sensing mechanism was discussed in detail. Importantly, the feasibility of this composite for sensing doxycycline in a simulated biological system and sensing MnO4 - in tap water was investigated.

One-pot synthesis of water-soluble near-infrared fluorescence RNase A capped CuInS2 quantum dots for in vivo imaging

Near-infrared (NIR) quantum dots (QDs) have been treated as a promising candidate of imaging agents for NIR fluorescence-guided surgery. Here, the RNase A-CuInS₂ QDs is good candidate, which performers well in gastrointestinal system imaging.

Heteroatom-doped carbon dots: synthesis, characterization, properties, photoluminescence mechanism and biological applications

Heteroatom-doped carbon dots (CDs), due to their excellent photoluminescence (PL) properties, attracted widespread attention recently and demonstrated immense promise for diverse applications, particularly for biological applications. The objective of this feature article is to provide a comprehensive overview of the recent progress in the research and development of heteroatom-doped CDs and a detailed description of the influence of single or co-doping heteroatoms on their PL behavior. The most recent understanding and critical insights into the PL mechanism of heteroatom-doped CDs are also highlighted. Moreover, potential bio-related applications of heteroatom-doped CDs in biosensing, bioimaging, and theranostics are also reviewed. This state-of-the-art review will provide a platform for understanding the intricate details of heteroatom-doped CDs, a summary of the latest progress in the field, and related applications in biology and is expected to inspire further developments in this exciting class of materials.

A novel triphenylamine-BODIPY dendron: click synthesis, near-infrared emission and a multi-channel chemodosimeter for Hg2+ and Fe3+

A novel near-infrared emission triphenylamine-BODIPY dendron for Hg²⁺ and Fe³⁺ detection, fluorescent nanoparticle and living cell imaging.

A near IR photosensitizer based on self-assembled CdSe quantum dot-aza-BODIPY conjugate coated with poly(ethylene glycol) and folic acid for concurrent fluorescence imaging and photodynamic therapy

Nanocomposite comprised of CdSe quantum dot-thiophene-substituted aza-BODIPY conjugate coated with FA and PEG has been developed for simultaneous fluorescence imaging and photodynamic therapy of HeLa cells via Förster resonance energy transfer.