Afterglow Nanoprobe-Enabled Quantitative Lateral Flow Immunoassay by a Palm-Size Device for Household Healthcare

Lateral flow immunoassay (LFIA), a classical point-of-care testing (POCT) technique, plays an important role in disease screening and healthcare monitoring. However, traditional LFIA is either designed for qualitative analysis or requires expensive equipment for quantification, limiting its use in household diagnosis. In this study, we proposed a new generation of LFIA for household health monitoring by using ultralong organic phosphorescence (UOP) nanomaterials as afterglow nanoprobes with a self-developed palm-size sensing device. The UOP nanoprobes exhibit a phosphorescence signal with a second-level lifetime, which completely avoids the interference from excitation light and biological background fluorescence. Therefore, an ultraminiaturized and low-cost UOP nanosensor was successfully designed by eliminating the complex optical path and filtering systems. We chose an inflammatory factor, C-reactive protein (CRP), for household POCT validation. The whole analysis was completed within 9 min. A limit of detection (LOD) of 0.54 ng/mL of CRP antigen was achieved with high stability and good specificity, which is comparable to laboratory instruments and fully satisfying the clinical diagnosis requirement.

Rapid Preparation of Fluorescent Carbon Dots from Pine Needles for Chemical Analysis

Fluorescent carbon dots with blue, green, and red emissions were rapidly prepared from modified pine needles through microwave irradiation in a one-pot reaction. The fluorescence intensity and emission versatility for a carbon source were experimentally optimized. The reaction times were under 10 min and the reaction temperatures were lower than 220 °C. Potential applications of magnetic fluorescence-linked immunoassays of carcinoembryonic antigen (CEA) and tumor necrosis factor-alpha (TNF-α) were presented. The detection limits for CEA and TNF-α (3.1 and 2.8 pg mL^-1, respectively) are lower than those presented in other reports, whereas the linear ranges for CEA and TNF-α (9 pg mL^-1 to 18 ng mL^-1 and 8.5 pg mL^-1 to 17 ng mL^-1, respectively) are wider than those presented in other reports. Magnetic immunoassays with fluorescent CD_s prepared from pine needles can enable rapid, sensitive, and selective detections for biochemical analysis.

Native llama Nanobody Library Panning Performed by Phage and Yeast Display Provides Binders Suitable for C-Reactive Protein Detection

C-reactive protein (CRP) is an inflammation biomarker that should be quantified accurately during infections and healing processes. Nanobodies are good candidates to replace conventional antibodies in immunodiagnostics due to their inexpensive production, simple engineering, and the possibility to obtain higher binder density on capture surfaces. Starting from the same pre-immune library, we compared the selection output resulting from two independent panning strategies, one exclusively exploiting the phage display and another in which a first round of phage display was followed by a second round of yeast display. There was a partial output convergence between the two methods, since two clones were identified using both panning protocols but the first provided several further different sequences, whereas the second favored the recovery of many copies of few clones. The isolated anti-CRP nanobodies had affinity in the low nanomolar range and were suitable for ELISA and immunoprecipitation. One of them was fused to SpyTag and exploited in combination with SpyCatcher as the immunocapture element to quantify CRP using electrochemical impedance spectroscopy. The sensitivity of the biosensor was calculated as low as 0.21 μg/mL.

Development of a Point-of-Care System Based on White Light Reflectance Spectroscopy: Application in CRP Determination

The development of methods and miniaturized systems for fast and reliable quantitative determinations at the Point-of-Care is a top challenge and priority in diagnostics. In this work, a compact bench-top system, based on White Light Reflectance Spectroscopy, is introduced and evaluated in an application with high clinical interest, namely the determination of C-Reactive protein (CRP) in human blood samples. The system encompassed all the necessary electronic and optical components for the performance of the assay, while the dedicated software provided the sequence and duration of assay steps, the reagents flow rate, the real-time monitoring of sensor response, and data processing to deliver in short time and accurately the CPR concentration in the sample. The CRP assay included two steps, the first comprising the binding of sample CRP onto the chip immobilized capture antibody and the second the reaction of the surface immunosorbed CRP molecules with the detection antibody. The assay duration was 12 min and the dynamic range was from 0.05 to 200 μg/mL, covering both normal values and acute inflammation incidents. There was an excellent agreement between CRP values determined in human plasma samples using the developed device with those received for the same samples by a standard diagnostic laboratory method.

"Lighting-up" curcumin nanoparticles triggered by pH for developing improved enzyme-linked immunosorbent assay

In the field of precision medicine, the anticipated features of ideal drug delivery systems (DDS) have high drug loading capacity and effective stimuli-triggered mechanism, which are fitting well with the expected merits of signal labels for enhanced enzyme-linked immunosorbent assay (ELISA). Inspired by this, poly (diallyldimethylammonium chloride)-capped curcumin nanoparticles (PDDA@CUR NPs) with high loading capacity were synthesized as signal labels and further applied to dual-model colorimetric and fluorescence ELISA for the detection of C-reactive protein (CRP). Curcumin (CUR) was elaborately selected as report molecule similar to the roles of drugs in DDS, which dispersed in neutral water exhibits a negligible fluorescence response due to the aggregation of CUR molecules induced quenching effect, stimulated by basic water (BW, pH 12.36), the allochroic effect from colorless to orange occurred and fluorescence restored because of the keto-enol tautomerism in the molecular structure of CUR, just like lighting-up (from signal "OFF" to signal "ON"), yielded a dual-model colorimetric and fluorescent signal readout. PDDA, as a polycationic electrolyte, provided a biological platform that is capable of interacting with CRP label antibodies by virtue of its positive centers. The results show that "lighting-up" CUR NPs-based dual-modal colorimetric and fluorescent ELISA for CRP detection has the merits of easy-to-use, good enough sensitivity and reliability. And more importantly, it brings innovative ideas for the precise identification and quantification of protein biomarkers.

Photoluminescence-based immunochemical methods for determination of C-reactive protein and procalcitonin

Modern, sensitive, rapid, and selective analytical methods for the detection of inflammatory markers are a crucial tool for the assessment of inflammation state, efficacy of medical intervention, and the prediction of future diseases. Their development requires understanding of current state for point-of-care testing of inflammatory markers and identification of their crucial drawbacks. This review summarizes the progress in the application of luminescent labels for immunoassays. The luminescent labels became more popular in the latest decade due to their high sensitivity, selectivity, and robustness. This review presents a constructive analysis of different luminescent labels such as fluorescent organic dyes, quantum dots, long-lived emissive nanoparticles, and up-converting nanocrystals, as well as a range of the strategies for inflammatory markers determination. The advantages and disadvantages of all classes of luminescent labels are demonstrated, and the strategies of labels modification for their improvement are discussed. The current approaches for the creation of luminescent probes and robust assays are also highlighted.

On-the-fly rapid immunoassay for neonatal sepsis diagnosis: C-reactive protein accurate determination using magnetic graphene-based micromotors

Based on the exceptional and new opened biosensing possibilities of self-propelled micromotors, a micromotor-based immunoassay (MIm) has smartly been designed for C-reactive protein (CRP) determination in plasma of preterm infants with sepsis suspicion. The design of the micromotors involved the electrosynthesis of a carbon-based outer layer (for antibody functionalization), an intermediate Ni layer (for magnetic guidance and stopped flow operations) and PtNPs inner catalytic layer (for catalytic bubble propulsion). Micromotors biofunctionalization on the outer layer (using carbon black (CB), reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs), and biocompatible propulsion capabilities, were carefully studied. Magnetic rGO/Ni/PtNPs micromotors exhibited the most efficient and reproducible (CV = 9%) anti-CRP functionalization, controlled stopped-flow operations as well as efficient bubble propulsion (1% H₂O₂, 1,5% NaCh, speed 140 μm s^-1). Analytical performance of MIm was excellent, allowing the direct (without dilution), sensitive (LOD = 0.80 μg/mL), and accurate CRP determination (E_r = 1%) in hardly available preterm babies' plasma samples with suspected sepsis using very low volumes (<10 μL) and in just 5 min of on-the-fly bioassay. Overall, the results obtained allowed the fast and reliable sepsis diagnostics in preterm babies' individuals with suspected sepsis, not only proving the usefulness of the approach as its potential utilization as point-of-care device for clinical analysis but drawing new horizons in extremely low sample volumes-based diagnostics.

A magneto-microfluidic platform for fluorescence immunosensing using quantum dot nanoparticles

This study reports the online fluorescent detection of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) biomarker proteins in microfluidic channels using functional nanoparticles. Functional magnetic nanoparticles labeled with two antibodies were predeposited on separated microfluidic channels. Antigens were passed through each microfluidic channel to react with the respective antibodies. Two types of fluorescent nanoparticles labeled with antibodies were then used to detect and confirm antigens in the immunocomplex. Results indicate that online fluorescent detection of proteins can provide advantages for real-time monitoring and diagnostic applications. The running time was less than 20 min for each trial. The detection limits of CEA and AFP were found to be 0.6 and 0.2 pg ml^-1. These detection limits are lower than those of ELISA. The linear ranges of CEA and AFP detection were from 1.8 pg ml^-1 to 1.8 ng ml^-1 and from 0.68 pg ml^-1 to 0.68 ng ml^-1 for two deposition zones in a magnetic sandwich immunoassay. The linear ranges of this method are wider than those of ELISA and those of most other methods. The measurements of CEA and AFP in serum samples from this method differed from ELISA results by 11% and 9.4%, respectively. The detection limit of online detection has achieved the same range as those of previous offline detection. This method has a good potential for automation and multichannel analysis to increase the throughput with some modifications in the future. The proposed method can provide simple, fast, and sensitive online detection for biomarkers.

A novel nanozyme assay utilising the catalytic activity of silver nanoparticles and SERRS

Artificial enzymes have become an increasingly interesting area of research due to their many advantages over natural protein enzymes which are expensive, difficult to isolate and unable to stand harsh environments. An important area of this research involves using metal nanoparticles as artificial enzymes, known as nanozymes, which exhibit peroxidase-like activity enabling them to catalyse the oxidation of substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂), giving a colorimetric response. Here we exploit the catalytic activity of silver nanoparticles (Ag NPs) in a surface based silver-linked immunosorbent assay (SLISA) to detect human C-reactive protein (CRP), an inflammatory marker. Ag NPs were conjugated to antibodies with specific recognition for the corresponding target antigenic molecule, CRP, and the Ag NPs were used to catalyse the oxidation of TMB by H₂O₂. The resulting coloured oxidation product was detected using SERRS. We demonstrate that Ag NPs can replace the enzymes used in a conventional ELISA and a detection limit of 1.09 ng mL^-1 of CRP can be achieved. It indicates the promise for SLISAs for biomarker detection and opens the way for further assays of this nature to be created. This novel assay has the potential to be optimised to detect lower levels of CRP and can be further extended for the sensitive and specific detection of other relevant biomarkers.

Ultrasensitive Detection of Protein with Wide Linear Dynamic Range Based on Core-Shell SERS Nanotags and Photonic Crystal Beads

Detection of proteins in a wide concentration range from fg mL^-1 to sub mg mL^-1 is a challenge in the high throughput analysis of precision medicine. Herein, we proposed a biosensor consisting of core-shell surface-enhanced Raman scattering (SERS) nanotags as labels and photonic crystal beads (PCBs) as carriers for ultrasensitive detection of proteins. In practice, Raman dyes (RDs) were embedded in the interface of gold core and silver shell in the bimetal nanoparticles to form SERS nanotags. It was found that the sensitivity was significantly improved due to the enhanced Raman signal by the coupling of the core-shell structure and linear dynamic range (LDR) was extended owing to the high surface to volume ratio of PCBs as well. In addition, we also demonstrated that the biosensor exhibited fine stability and low background, which has great application potential in the detection of protein biomarkers.

Multiplexed detection of lung cancer biomarkers based on quantum dots and microbeads

We have developed a multiplexed fluoroimmunoassay of three lung cancer biomarkers based on multicolor quantum dots (QDs) as detection elements and micro-magnetic beads as immune carriers. QDs have the ability to simplify multiplexed analysis. In our method, the fluorescent signals derived from three cross-talk-free QD conjugated probes with emission maxima at 525, 585 and 625nm could be analyzed to determine the concentrations of the target proteins. With this system, fragments of cytokeratin 19 (CYRFA 21-1), carcinoembryonic antigen (CEA), and neuron-specific enolase (NSE), were simultaneously detected in a single sample with a low detection limit down to the 1.0ng/mL level (364pg/mL for CYRFA 21-1, 38pg/mL for CEA, 370pg/mL for NSE in a single detection). Additional advantages of the presented method include ease of operation, low cost, and a very low sample volume (20µL).

Surface Enhanced Raman Scattering Detection of Cancer Biomarkers with Bifunctional Nanocomposite Probes

This report describes new findings of an investigation of a bifunctional nanocomposite probe for the detection of cancer biomarkers, demonstrating the viability of magnetic focusing and SERS detection in a microfluidic platform. The nanocomposite probe consists of a magnetic nickel-iron core and a gold shell. Upon bioconjugation, the nanoprobes are magnetically focused on a specific spot in a microfluidic channel, enabling an enrichment of "hot spots" for surface enhanced Raman scattering detection of the targeted carcinoembryonic antigen. The detection sensitivity, with a limit of detection of ∼0.1 pM, is shown to scale with the magnetic focusing time and the nanoparticle size. The latter is also shown to exhibit an excellent agreement between the experimental data and the theoretical simulation. Implications of the findings to the development of rapid and sensitive microfluidic detection of cancer biomarkers are also discussed.

Rapid and quantitative detection of C-reactive protein based on quantum dots and immunofiltration assay

Convenient and rapid immunofiltration assays (IFAs) enable on-site "yes" or "no" determination of disease markers. However, traditional IFAs are commonly qualitative or semi-quantitative and are very limited for the efficient testing of samples in field diagnostics. Here, we overcome these limitations by developing a quantum dots (QDs)-based fluorescent IFA for the quantitative detection of C-reactive proteins (CRP). CRP, the well-known diagnostic marker for acute viral and bacterial infections, was used as a model analyte to demonstrate performance and sensitivity of our developed QDs-based IFA. QDs capped with both polyethylene glycol (PEG) and glutathione were used as fluorescent labels for our IFAs. The presence of the surface PEG layer, which reduced the non-specific protein interactions, in conjunction with the inherent optical properties of QDs, resulted in lower background signal, increased sensitivity, and ability to detect CRP down to 0.79 mg/L with only 5 µL serum sample. In addition, the developed assay is simple, fast and can quantitatively detect CRP with a detection limit up to 200 mg/L. Clinical test results of our QD-based IFA are well correlated with the traditional latex enhance immune-agglutination aggregation. The proposed QD-based fluorescent IFA is very promising, and potentially will be adopted for multiplexed immunoassay and in field point-of-care test.