Bimodal Detection Research Articles

Performance-complementary colorimetric/electrochemical bimodal detection of Hg2+ based on analyte-accelerated peroxidase-mimicking activity of GO-AuNPs

As a highly toxic heavy metal pollutant, mercury ions cause substantial risks to the environment and human health, and developing high-performance and convenient analytical approaches becomes quite important. Here we propose a performance-complementary colorimetric/electrochemical dual-mode Hg2+ sensing method based on the analyte accelerating the peroxidase-mimetic activity of gold nanoparticles (AuNPs) loaded on graphene oxide (GO). The GO-AuNPs composite was readily fabricated via mechanically mixing AuNPs and GO with controllable proportions, exhibiting a weak peroxidase-like activity in catalyzing the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB). Upon the introduction of Hg2+, it combined with AuNPs rapidly, significantly enhancing the peroxidase-mimicking activity of GO-AuNPs. By capturing the color signal of the generated blue oxTMB and the electro-oxidation response of residual TMB, a “turn-on” colorimetric and “turn-off” electrochemical bimodal method was established for Hg2+ measurement, providing a linear range of 10–60 μg/L in colorimetric detection and 0.001–20 μg/L in electrochemical analysis. Different from common bimodal assays mainly improving detecting reliability due to their cross-validation ability, our dual-mode sensor exhibits the unique feature of complementary sensitivity and detection range, thus enabling its flexible use in analyzing different levels of the target in a broad scope with no requirement for sample enrichment and dilution.

Depth-resolved elemental and molecular analysis of polymeric multilayers with EI-MS and ICP-OES using chemometric evaluation

Polymeric composite materials with layered structures have increasingly gained importance as, for specific applications, the required properties cannot be achieved with one single material; thus, for example, multi-layer polymers or special surface coatings are employed.None of the conventionally available techniques enables a comprehensive characterization of composite materials, including depth-resolved information about their organic and elemental constituents.In this work, a previously introduced approach enabling the direct characterization of the organic and inorganic constituents of solid polymer samples was further developed and optimized for depth profiling analysis of stacked layer polymers. For this purpose, the ablation chamber’s washout behavior and transfer line’s transport efficiency were improved. Chemometric methods were applied for the data analysis to gain greater insight and enable more precise differentiation, comparison and classification.The work investigates the feasibility of the developed approach by analyzing a multi-layer stacked polymer sample created from nail polishes and using cluster analysis on the data collected with the bimodal detection. The layers of the sample could be differentiated by their organic and elemental constituents’ fingerprints, achieving a depth resolution of 7 µm.

Multifunctional Nanocomposite Yield-Stress Fluids for Printable and Stretchable Electronics.

Compliant materials are crucial for stretchable electronics. Stretchable solids and gels have limitations in deformability and durability, whereas active liquids struggle to create complex devices. This study presents multifunctional yield-stress fluids as printable ink materials to construct stretchable electronic devices. Ionic nanocomposites comprise silica nanoparticles and ion liquids, while electrical nanocomposites use the natural oxidation of liquid metals to produce gallium oxide nanoflake additives. These nanocomposite inks can be printed on an elastomer substrate and stay in a solid state for easy encapsulation. However, their transition into a liquid state during stretching allows ultrahigh deformability up to the fracture strain of the elastomer. The ionic inks produce strain sensors with high stretchability and temperature sensors with high sensitivity of 7% °C-1. Smart gloves are further created by integrating these sensors with printed electrical interconnects, demonstrating bimodal detection of temperatures and hand gestures. The nanocomposite yield-stress fluids combine the desirable qualities of solids and liquids for stretchable devices and systems.

Self-reduced MXene-Metal interaction electrochemiluminescence support with synergistic electrocatalytic and photothermal effects for the bimodal detection of ovarian cancer biomarkers

Novel two-dimensional MXene with unique optical and electrical properties has become a new focus in the field of sensing. In particular, their metallic conductivity, good biocompatibility and high anchoring ability to biomaterials make them attractive candidates. Despite such remarkable properties, there are certain limitations, such as low oxidative stability. MXene-Metal interactions are an effective strategy to maintain the long-term stability of MXene, while also improving the electrochemical activity and optical properties. Herein, a series of MXene/Ag nanocomposites including Ti3C2/Ag, Nb2C/Ag and V2C/Ag were designed based on the surface chemistry characteristics of MXene, where MXene served as the substrate for in-situ growth of silver nanoparticles via self-reduction of Ag(NH3)2+. The results showed that V2C MXene has the strongest self-reducing ability due to its multiple variable valence states, larger interlayer space and more reactive groups. Moreover, V2C/Ag exhibited unexpected oxygen reduction reaction catalytic activity and photothermal performance. In view of which, an electrochemiluminescence-photothermal (ECL-photothermal) immunosensor was developed using V2C/Ag as ECL anchor and photothermal reagent for ultrasensitive detection of Lipolysis stimulated lipoprotein receptor. This work not only provides a simple and effective synthesis method of MXene supported metal nanocomposites, but also provides more inspirations for exploring the efficient biosensing strategies.

Bio-conjugated carbon dots for the bimodal detection of prostate cancer biomarkers via sandwich fluorescence and electrochemical immunoassays.

Bimodal detection facilitates the accurate and reliable detection of cancer biomarkers, which can assist in the early diagnosis of cancer. Herein, S-doped carbon dots (OCDs) with a size of 3 nm and blue emission were synthesized by the hydrothermal treatment of onion extract. The S-doped carbon dots were bioconjugated with an antibody (OCDs@PSAAbHRP) to design a nanoprobe for the detection of prostate specific antigen (PSA), an important serum based prostate cancer biomarker. The detection probe enabled the biomodal assay of PSA via fluorescence immunoassay (FIA) and electrochemical immunoassay (ECIA). In both assays, polyethylenimine stabilized polyaniline nanoparticles (PNPs) were used as the immobilization matrix, which played a major role in widening the linear range of biosensors (0.1 to 100 ng ml-1 for ECIA and 5 to 120 ng ml-1 for FIA). Paper-based and smartphone-integrated fluorescence immuno-array developed using the OCDs@PSAAbHRP detection probe provided cost-effective and rapid detection, while the electrochemical immunoassay provided a high sensitivity (7.8 μA ng-1 ml-1 cm-2) and low detection limit (38 pg ml-1) for PSA detection. The role of OCDs in enhancing the sensor performance was deciphered by carrying out detailed electrochemical studies with HRP enzyme-loaded OCDs. The biosensor was used to detect PSA in human blood serum samples and the results were consistent with conventional techniques. Owing to its analytical properties coupled with simplicity, cost-effectiveness, and portability, the bimodal sensor system has potential for application in clinical analysis.

Palladium nanoclusters as a label to determine GFAP in human serum from donors with stroke by bimodal detection: inductively coupled plasma-mass spectrometry and linear sweep voltammetry

Water-soluble, stable, and monodisperse palladium nanoclusters (PdNCs) were synthesized using NaBH4 as a reductant and lipoic acid as a ligand. PdNCs, measured by high-resolution transmission electron microscopy, showed a round shape and a diameter of 2.49 ± 0.02 nm. It was found that each PdNC contains 550 Pd atoms on average. These PdNCs offer high amplification as a label of biochemical reactions when inductively coupled plasma-mass spectrometry (ICP-MS) is used as a detector. In addition, PdNCs have catalytic activity on electrochemical reactions, allowing detection by linear sweep voltammetry (LSV). As a proof of applicability, a competitive immunoassay based on PdNC labels was developed for the determination of glial fibrillary acidic protein (GFAP) in human serum, comparing ICP-MS and LSV detection. GFAP is a biomarker for differentiating between patients with ischemic stroke (IS) and hemorrhagic stroke (HS). The limit of detection (LoD), corresponding to IC10 (4-parameter logistic curve), was 0.03 pM of GFAP, both by ICP-MS and LSV, being lower than the 0.31 pM LoD provided by the ELISA commercial kit. Using the error profile method, 0.03 pM and 0.11 pM LoDs were obtained respectively by ICP-MS and LSV: LoD is lower by ICP-MS due to the better precision of the measurements. The analyses of human serum samples from IS, HS, and control (CT) donors using PdNC labels and detection by ICP-MS and LSV were validated with a commercial ELISA kit (for CT donors only ICP-MS provided enough sensitivity). Results point out toward the future use of PdNCs as a label in other immunoprobes for the determination of specific proteins requiring very low LoDs as well as the development of electrochemical decentralized methodologies.Graphical

Cheap and portable paper chip with terrific oxidase-like activity and SERS enhancement performance for SERS-colorimetric bimodal detection of intracellular glutathione

Glutathione (GSH) acts a crucial role in the normal operation of manifold life activities and is closely bound up with many human diseases. Here, a SERS-colorimetric bimodal paper-based biosensor based on Mn-doped CDs/silver nanoparticles (Mn-CDs/AgNPs) has been fabricated for high-efficiency quantification of intracellular GSH. The Mn-CDs/AgNPs with fine oxidase-like characteristic and SERS enhancement ability has been assembled onto the Whatman filter paper (WFP) to cleverly fabricate paper chip (Mn-CDs/AgNPs@WFP) which can trigger the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue TMBox and simultaneously enhance the SERS signal of TMBox. However, the introduction of GSH inhibits the oxidation of TMB, leading to color fading of paper chip and diminishment of SERS signal. Considering this, the bimodal paper-based sensing platform can be exploited for SERS-colorimetric detection of GSH, manifesting excellent selectivity, reliable stability, and satisfactory precision. The detection limits of SERS and colorimetric detection modes are as low as 0.41 μM and 0.53 μM, respectively. Furthermore, this proposed bimodal biosensor has been successfully utilized for the determination of intracellular GSH and validated by commercial GSH assay kit, which provides a mighty and convenient tool for intracellular GSH detection and can boost future effort about exploitation of other multimode paper-based biosensors as well as promote their appliances in disease diagnosis.

β-cyclodextrin based platform for bimodal detection of o-toluidine and cholesterol: Electrochemical and fluorescence sensing

β-cyclodextrin based platform for bimodal detection of o-toluidine and cholesterol: Electrochemical and fluorescence sensing

Fully automated thyroid ultrasound screening utilizing multi-modality image and anatomical prior

There is a high prevalence of thyroid nodules in the general population. Early detection is essential for the treatment of malignant thyroid nodules. Ultrasound has the advantage of being non-invasive and radiation-free, and is sufficient for early diagnosis of malignant nodules. However, ultrasound image acquisition relies on manual manipulation of the probe by the sonographer, making it difficult to screen populations for malignant thyroid nodules. Robotic ultrasound systems (RUS) are expected to replace sonographers in ultrasound scanning and improve the standardization and reproducibility of ultrasound examinations. However, there is currently no RUS that can fully autonomously screen for thyroid nodules. In this paper, we propose a fully automated two-step search method that mimics a physician's thyroid scanning protocol. First, using the body surface structure observed by the RGBD camera, we use a bimodal detection network for the initial localization of the human neck. The bimodal detection network achieves an average accuracy of 0.986. Second, we designed a tracking strategy based on the anatomical prior of the human neck to navigate the probe for thyroid ultrasound acquisition. An network-based visual servoing method enables shadow prevention and target tracking to be performed uniformly. In vitro experiments demonstrated the effectiveness of the protocol.

Enhanced oxidase-mimic constructed by luminescent carbon dots loaded on MIL-53(Fe)-NO2 for dual-mode detection of gallic acid and biothiols in food and humans

Monitoring of gallic acid (GA) in food and biothiols in humans is crucial for body health. Nanozyme-mediated colorimetric strategy for evaluating them has been widely applied nowadays, however, the inferior efficient and susceptible single-signal recognition limit its further application. Herein, a sensitive biosensor was first constructed for bimodal detection of GA and biothiols based on CDs@MIL-53(Fe)-NO2, prepared through a facile and time-saving microwave treatment. Benefiting from the excellent fluorescent and electron transfer properties of CDs, CDs@MIL-53(Fe)-NO2 exhibited significant enhanced blue fluorescence and oxidase-like activity, which could oxide colorless 3,3′,5,5′-tetramethylbenzidine without H2O2, and the blue product could quench the fluorescence of composite. The dual-mode assay based on such bifunctional nanozyme showed an extremely sensitivity towards GA/l-cysteine/homocysteine with the detection limit of 62/65/124 nM and 17/16/27 nM in colorimetric/fluorescent modes, respectively. The practicability in real samples and portability based on a smartphone of the analysis has been investigated with reliable results.

Rail Surface Defect Detection Through Bimodal RSDINet and Three-Branched Evidential Fusion

Current state-of-the-art intensity and depth modal-based railway surface defect inspection system faces the dilemma between false alarming and miss detection. To overcome this challenge, a bimodal detection scheme using both feature-level fusion and (evidence theory-based) decision-level fusion is designed. Moreover, an improved evidential fusion algorithm is proposed, which adopts three-branched evidential weight structure and introduces the Transferable Belief Model to the improved decision functions, achieving outstanding performance on effectiveness and robustness analysis. Both theoretical justifications and experimental results validate the efficiency of the hybrid fusion-based detection scheme in solving rail surface defect problems.

Hierarchical unimodal processing within the primary somatosensory cortex during a bimodal detection task

Do sensory cortices process more than one sensory modality?To answer these questions, scientists have generated a wide variety of studies at distinct space-time scales in different animal models, and often shown contradictory conclusions. Some conclude that this process occurs in early sensory cortices, but others that this occurs in areas central to sensory cortices. Here, we sought to determine whether sensory neurons process and encode physical stimulus properties of different modalities (tactile and acoustic). Forthis, we designed a bimodal detection task where the senses of touch and hearing compete from trial to trial. Two Rhesus monkeys performed this novel task, while neural activity was recorded in areas 3b and 1 of the primary somatosensory cortex (S1). Weanalyzed neurons' coding properties and variability, organizing them by their receptive field's position relative to the stimulation zone. Our results indicate that neurons of areas 3b and 1 are unimodal, encoding only the tactile modality in both the firing rate and variability. Moreover, we found that neurons in area 3b carried more information about the periodic stimulus structure than those in area 1, possessed lower response and coding latencies, and had a lower intrinsic time scale. In sum, these differences reveal a hidden processing-based hierarchy. Finally, using a powerful nonlinear dimensionality reduction algorithm, we show that the activity from areas 3b and 1 can be separated, establishing a clear division in the functionality of these two subareas of S1.

Tailoring dual-functional gold nanoplasmonic rods for colorimetric and SERS detection of mercury species in complex matrices

Mercury speciation is essential for ecological security and human health due to its accumulative, toxicity, and persistent feature in the environment and biota. Here, we present a bimodal detection strategy for discrimination of mercury ions (Hg2+) and methylmercury (CH3Hg+) by utilizing valence-states mediated morphology transition of p-aminothiophenol (PATP) modified gold nanorods (GNRs@PATP). Hg2+ could be reduced by PATP to form Au-Hg amalgams on the surface of GNRs. The nanoalloy prevents GNRs aggregation, exhibiting a blue-shift of longitudinal surface plasmon resonance peak. Furthermore, the presence of Hg2+ triggers conversions of PATP to p, p′‑dimercaptoazobenzene, which results in a distinctly surface enhanced Raman scattering (SERS) signals output. Conversely, CH3Hg+ reacts with the amino of the PATP and facilitates GNRs self-assembly due to the excellent affinity of CH3Hg+-NH2 interactions, leading to occurrence of an absorption peak at 930 nm. Based on the to-together-and-to-isolate interaction between GNRs@PATP and mercury species, a “turn-on” SERS method and colorimetric assay are developed for Hg2+ and CH3Hg+ detection, respectively, providing LOD of 3.2 fM for Hg2+ and 0.3 nM for CH3Hg+. This sensing system displays a high selective response towards Hg2+ and CH3Hg+. Its practical applications are further validated by mercury speciation in environmental water, food and human hair.

Multifeature Fusion Tracking Algorithm Based on Self-Associative Memory Learning Mechanism

A multi-feature fusion tracking algorithm updated with a self-associative memory learning mechanism is proposed to address the problems of short-time disappearance, re-emergence of the target and instability of single features in the kernelized correlation filtering algorithm. When extracting features, directional gradient histogram features, color features, and scale invariant features are fused instead of single features to collect more features of the target and increase the feature robustness. In the detection stage, the bimodal detection is proposed to judge whether the target model needs updating. Bimodal detection is used to judge the maximum target response in the search domain and predict the location of the target in the next frame. The self-associative memory learning mechanism was added into the updating template, and the original algorithm framework was improved to cope with the change of target model. The new algorithm update is biogenic, can recover fragment information, deal with complex and changeable tracking situation. Simulation experiments were conducted on the OTB50, OTB100, and UAV123 video datasets for the classical and new algorithms. The simulation verified that the proposed tracking algorithm has a high success and accuracy rate, which has research value. The tracking success rate improved by 23.6% and the accuracy rate improved by 18.8%.

Enantiopure chiroptical probes for circular dichroism and absorbance based detection of nerve gas simulants

A series of oxovanadium(V) compounds 1-4 were prepared and explored as stereodynamic chiroptical probes to detect a simulant of sarin known as diethyl chlorophosphate (DCP) without any interference from the competing analytes. Simultaneous CD cum UV/vis based bimodal instant recognition of DCP using optically active probes is unprecedented. Upon fabricating the vanadium compound with a polymer has yielded a chiroptical membrane, which showed a change in its dichroic as well as colorimetric signals on interaction with DCP vapour at 1 ppm. EPR and UV/vis studies revealed an irreversible change of the CD-active V(V) to the CD-silent ternary V(V) species in presence of DCP via a transient V(IV) species. Nucleophilic attack of the alkoxo oxygen of 1-4 to the electrophilic P atom of DCP resulted in the formation of ternary V(V) compounds as confirmed by 51V/31P NMR.

Multifunctional N-Doped Carbon Dots for Bimodal Detection of Bilirubin and Vitamin B12, Living Cell Imaging, and Fluorescent Ink.

A N-doped carbon dot (NCD) has been synthesized via a simplistic one-step hydrothermal technique using l-aspartic acid and 3,6-diaminoacridine hydrochloride. The NCDs exhibit a high quantum yield (22.7%) and excellent optical stability in aqueous media. Additionally, NCDs display good solid-state yellowish-green emission and are suitable for security ink applications. The remarkable fluorescence (FL) properties of NCDs are further applied to develop a multifunctional sensor for bilirubin (BR) and vitamin B12 (VB12) via fluorescence quenching. We have systematically studied the FL quenching mechanisms of the two analytes. The primary quenching mechanism of BR is via the Förster resonant energy transfer (FRET) pathway facilitated by the H-bonding network between the hydrophilic moieties existing at the surface of BR and NCDs. In contrast, the inner filter effect (IFE) is mainly responsible for the recognition of VB12. The practicability of the nanoprobe NCDs is further tested in real-sample analysis for BR (human serum and urine samples) and VB12 (VB12 tablets, human serum, and energy drink) with a satisfactory outcome. The in vitro competency is also verified in the human cervical cancer cell line (HeLa cell) with negligible cytotoxicity and significant biocompatibility. This result facilitates the application of NCDs for bioimaging and recognition of VB12 in a living organism.

Fluorescence and electrochemical assay for bimodal detection of lead ions based on Metal–Organic framework nanosheets

The accurate measurement of heavy metal ions is essential for human health and environmental protection. Here, we report the design of a simple and convenient bimodal strategy for signal-on, label-free lead ion detection in environmental samples based on two-dimensional metal–organic framework (2D-MOF) nanosheets. 2D-MOFs have different affinities toward guanine-rich DNA (ssGDNA) and the G-quadruplex, allowing these structures to be distinguished. The nanosheets were also used as quenchers for fluorescent lead ion detection. Using lead ions to induce G-quadruplex formation from ssGDNA, a simple fluorescence resonance energy transfer (FRET) strategy was developed for lead ion detection; the detection limit was 3.3 nM. Based on changes in the GDNA configuration, the FRET system was converted into an electrochemical sensor for lead ion assays using an electrode modified with the 2D-MOF nanosheets. Electrochemical impedance spectroscopy showed a high sensitivity and a low limit of detection (i.e., 8.7 pM) of the electrode. The adaptability of the bimodal mechanism was verified through the successful detection of lead ions in tap water and fertilizer samples, and the method accuracy was demonstrated through inductively coupled plasma analysis. The developed bimodal device is cost-effective, highly sensitive, and allows for convenient operation, thereby rendering it a promising and reliable system for the detection of lead ions in environmental samples.

Sources of variation and establishment of Russian reference intervals for major hormones and tumor markers

A multicenter study was organized to explore sources of variation (SVs) of reference values (RVs) for 22 major immunochemistry analytes and to determine reference intervals (RIs) for the Russian population. According to IFCC Committee on Reference Intervals and Decision Limits (C-RIDL) protocol, 758 healthy volunteers were recruited in St. Petersburg, Moscow, and Yekaterinburg. Serum samples were tested for five tumor markers, 17 hormones and related tests by Beckman Coulter's UniCel DxI 800 immunochemistry analyzer. SVs were explored using multiple regression analysis and ANOVA. Standard deviation ratio (SDR) of 0.4 was used as primary guide for partitioning RIs by gender and age. SDR for between-city difference was <0.4 for all analytes. Secondary exclusion of individuals was done under the following conditions: for female sex-hormones, those with contraceptives (8%); for CA19-9, those supposed to have negative Lewis blood-group (10.5% males and 11.3% females); for insulin, those with BMI≥28 kg/m2 (31%); for the thyroid panel, those with anti-thyroid antibodies (10.3% males; 24.5% females), for CEA those with smoking habit (30% males and 16% females). Gender-specific RIs were required for all analytes except CA19-9, CA15-3, thyroid-related tests, parathyroid hormone, and insulin. Age-specific RIs were required for alpha-fetoprotein, CEA, all sex-hormones for females, FSH and progesterone for both sexes. RIs were generally derived by parametric method after Gaussian transformation using modified Box-Cox formula. Exceptions were growth hormone, estradiol for females in postmenopause, and progesterone for females in premenopause, for which nonparametric method was required due to bimodal distribution and/or insufficient detection limit. RIs for major hormones and tumor markers specific for the Russian population were derived based on the up-to-date internationally harmonized protocol by careful consideration of analyte-specific SVs.

Self-Assembled Extended π-Systems for Sensing and Security Applications.

Molecules and materials derived from self-assembled extended π-systems have strong and reversible optical properties, which can be modulated with external stimuli such as temperature, mechanical stress, ions, the polarity of the medium, and so on. In many cases, absorption and emission responses of self-assembled supramolecular π-systems are manifested several times higher when compared with the individual molecular building blocks. These properties of molecular assemblies encourage scientists to have a deeper understanding of their design to explore them for suitable optoelectronic applications. Therefore, it is important to bring in highly responsive optical features in π-systems, for which it is necessary to modify their structures by varying the conjugation length and by introducing donor-acceptor functional groups. Using noncovalent forces, π-systems can be put together to form assemblies of different shapes and sizes with varied optical band gaps through controlling intermolecular electronic interactions. In addition, using directional forces, it is possible to bring anisotropy to the self-assembled nanostructures, facilitating efficient exciton migration, resulting in the modulation of optical and electron-transport properties. In this Account, we mainly summarize our findings with optically tunable self-assemblies of extended π-systems such as p-phenylenevinylenes (PVs), p-phenyleneethynylenes (PEs), and diketopyrrolopyrroles (DPPs) as different stimuli-responsive platforms to develop sensors and security materials. We start with how PV self-assemblies and their coassemblies with appropriate electron-deficient systems can be used for the sensing of analytes in contact mode or in the vapor phase. For example, whereas the PV having electron-deficient terminal groups has high sensitivity toward trinitrotoluene (TNT) in contact mode, the supercoiled fibers formed by the coassembly of self-sorted stacks of C3-symmetrical PV and C3-symmetrical electron-deficient perylene bisimide are capable of sensing vapors of nitrobenzene and o-toluidine. The power of different functional groups in combination with PVs has been further illustrated by attaching CO2-sensitive tertiary amine moieties to a cyano-substituted PV, which allowed the bimodal detection of CO2 using fluorescence and Raman spectroscopy. Interestingly, the functionalization of PVs with terminal amide groups and chiral alkoxy side chains provided a mechanochromic system that allows self-erasable imaging. Whereas PVs exhibit quenching of fluorescence in most cases during self-assembly, PE derivatives exhibit aggregation-induced emission. This property of PEs has been exploited for the development of stimuli-responsive security materials, especially for currency and documents. For instance, the blue fluorescence of a PE attached to hydrophilic oxyethylene side chains coated on a filter paper upon contact with water changes to cyan emission due to the change in the molecular packing. Interestingly, the molecular packing of a Bodipy-attached PE-based gelator allowed a stress-induced change in the emission behavior, resulting in strong near-infrared (NIR) emission upon the application of mechanical stress or gelation. Finally, the use of DPP-based π-systems for the development of NIR transparent optical filters that block UV-vis light and their security- and forensic-related applications are described. These selected examples of the π-system self-assemblies provide an idea of the current status and future opportunities for scientists interested in this field of self-assembly and soft materials research.

Dual-probe (colorimetric and fluorometric) detection of ferritin using antibody-modified gold@carbon dot nanoconjugates.

A dual-mode assay is described for immunological determination of the anemia biomarker ferritin. It is based on the use of a gold@carbon dot (Au@CD) nanoconjugate as a colorimetric and fluorescent probe. Au@CD is hydrophilic, easily surface modified and stable in aqueous solution. The Au@CD have a red color with blue-green fluorescence and were modified with antibody against ferritin. This allows bi-modal detection of ferritin. Assays can be performed in phosphate buffer and were also analyzed in (Bovine Serum Albumin) BSA and (Fetal Bovine Serum) FBS. Detection is based on antigen-antibody interaction underlying the classical sandwich model. Response to ferritin can be detected by spectrophotometry (at 570nm) or fluorescence (at excitation/emission maxima of 354/454nm). Under optimal conditions, the assay has a linear response in the 1 to 120ngmL-1 ferritin concentration range and detection limits of 20 ng (colorimetrically) and 64ng (fluorometrically). Graphical abstract Schematic representation of the function of the designed nanoprobe. The Au@CD nanoconjugates are functionalized with ferritin antibody in the initial step which specifically interacts with ferritin molecules leading to aggregation and subsequent changes in the optical and fluorescence signals.