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Chemiluminescence (CL) provides ideal conditions for point‐of‐care testing (POCT) with wide dynamic ranges, superior sensitivities, and detection simplicity. It has not arrived routinely in the POCT field due to naturally low quantum yields of typical probes and the lack of sensitive low‐cost detection devices. Here, we developed a universal microfluidic paper‐based analytical device (μPAD) using l‐lactate as model analyte. We demonstrate that a smartphone camera can compete with a scientific CCD camera as performance benchmark when using the strong CL emitter, m‐carboxy luminol, resulting in extraordinary signal‐to‐noise ratios of 67. The μPAD provides CV<10 %, stability at room temperature for≥3 months and simple processing. Furthermore, the μPAD enables the detection of picomoles of the luminophore providing additional design flexibility. Thus, this new CL‐μPAD is available for translating the many CL standard analytical assays performed in microtiter plates, microarrays or other more complex detection strategies to the POC. [ABSTRACT FROM AUTHOR]

Recent years have confirmed the ubiquitous applicability of lateral flow assays (LFA) in point-of-care testing (POCT). To make this technology available for low abundance analytes, strategies towards lower limits of detections (LOD), while maintaining the LFA's ease of use, are still being sought. Here, we demonstrate how liposomes can significantly improve the LOD of traditional gold nanoparticle (AuNP)–based assays while fully supporting a ready-to-use system for commercial application. We fine-tuned liposomes towards photometric and fluorescence performance on the synthesis level and applied them in an established interleukin 6 (IL-6) immunoassay normally using commercial AuNP labels. IL-6's low abundance (< 10 pg mL−1) and increasing relevance as prognostic marker for infections make it an ideal model analyte. It was found that liposomes with a high encapsulant load (150 mmol L−1 sulforhodamine B (SRB)) easily outperform AuNPs in photometric LFAs. Specifically, liposomes with 350 nm in diameter yield a lower LOD even in complex matrices such as human serum below the clinically relevant range (7 pg mL−1) beating AuNP by over an order of magnitude (81 pg mL−1). When dehydrated on the strip, liposomes maintained their signal performance for over a year even when stored at ambient temperature and indicate extraordinary stability of up to 8 years when stored as liquid. Whereas no LOD improvement was obtained by exploiting the liposomes' fluorescence, an extraordinary gain in signal intensity was achieved upon lysis which is a promising feature for high-resolution and low-cost detection devices. Minimizing the procedural steps by inherently fluorescent liposomes, however, is not feasible. Finally, liposomes are ready for commercial applications as they are easy to mass-produce and can simply be substituted for the ubiquitously used AuNPs in the POCT market. [ABSTRACT FROM AUTHOR]

Gold nanoparticle–catalyzed chemiluminescence (CL) of luminol is an attractive alternative to strategies relying on enzymes, as their aggregation leads to significantly enhanced CL signals. Consequently, analytes disturbing such aggregation will lead to an easy-to-quantify weakening of the signal. Based on this concept, a homogeneous aptamer-based assay for the detection of sulfadimethoxine (SDM) has been developed as a microfluidic CL flow-injection platform. Here, the efficient mixing of gold nanoparticles, aptamers, and analyte in short channel distances is of utmost importance, and two-dimensional (2D) and three-dimensional (3D) mixer designs made via Xurography were investigated. In the end, since 2D designs could not provide sufficient mixing, a laminated 3D 5-layer microfluidic mixer was developed and optimized with respect to mixing capability and observation by the charge-coupled device (CCD) camera. Furthermore, the performance of standard luminol and its more hydrophilic derivative m-carboxy luminol was studied identifying the hydrophilic derivative to provide tenfold more signal enhancement and reliable results. Finally, the novel detection platform was used for the specific detection of SDM via its aptamer and yielded a stunning dynamic range over 5 orders of magnitude (0.01–1000 ng/ml) and a limit of detection of 4 pg/ml. This new detection concept not only outperforms other methods for SDM detection, but can be suggested as a new flow-injection strategy for aptamer-based rapid and cost-efficient analysis in environmental monitoring and food safety. [ABSTRACT FROM AUTHOR]

Chemiluminescence (CL) provides outstanding analytical performance due to its independence from external light sources, background-free nature and exceptional sensitivity and selectivity. Yet, ultra-sensitive (bio)analysis is impeded by low hydrophilicity, poor quantum yields, fast kinetics or instability of most CL reagents such as luminol, acridinium esters, dioxetanes or peroxyoxalic derivatives. Photophysical studies show that m -carboxy luminol overcomes these limitations as its hydrophilic design provides a 5-fold increase in relative quantum yield resulting in superior performance in H 2 O 2 -dependent bioassays with 18-fold higher sensitivity for the quantification of its co-reactant H 2 O 2 , and 5-times lower detection limits for the luminophore. Studies with CL enhancers suggest its significance for mechanistic investigations in tandem with peroxidases. Finally, its integration into enzymatic and immunoassay applications demonstrates that m -carboxy luminol will provide signal enhancement, lower detection limits, and increased dynamic ranges for any other luminol-based CL assay, thus comprising the potential to replace luminol as benchmark probe. [Display omitted] • New CL probe excels in most relevant chemiluminescence (CL) bioassays benchmarked against luminol. • Continuous CL enhancement with m -carboxy luminol. • Characterization of photophysical properties and CL reaction understanding. • Comprehensive portfolio of optimized CL reaction conditions. [ABSTRACT FROM AUTHOR]

The most efficient and commonly used electrochemiluminescence (ECL) emitters are luminol, [Ru(bpy)3]2+, and derivatives thereof. Luminol stands out due to its low excitation potential, but applications are limited by its insolubility under physiological conditions. The water-soluble m-carboxy luminol was synthesized in 15 % yield and exhibited high solubility under physiological conditions and afforded a four-fold ECL signal increase (vs. luminol). Entrapment in DNA-tagged liposomes enabled a DNA assay with a detection limit of 3.2 pmol L−1, which is 150 times lower than the corresponding fluorescence approach. This remarkable sensitivity gain and the low excitation potential establish m-carboxy luminol as a superior ECL probe with direct relevance to chemiluminescence and enzymatic bioanalytical approaches. [ABSTRACT FROM AUTHOR]

Die effizientesten und meistgenutzten Elektrochemilumineszenz(ECL)-Moleküle sind Luminol, [Ru(bpy)3]2+ und dessen Derivate. Luminol zeichnet sich durch sein niedriges Anregungspotential aus, jedoch sind seine Anwendungen begrenzt aufgrund der sehr geringen Wasserlöslichkeit unter physiologischen Bedingungen. Das wasserlösliche m-Carboxyluminol wurde in einer Ausbeute von 15 % synthetisiert und erreicht neben einer hohen Löslichkeit unter physiologischen Bedingungen einen vierfachen ECL-Signalanstieg (gegenüber Luminol). Mittels Einschluss in DNA-modifizierte Liposome wurde ein DNA-Assay mit einer Nachweisgrenze von 3.2 pmol L−1 ermöglicht, die 150-fach niedriger ist als die Nachweisgrenze des entsprechenden Fluoreszenzassays. Diese bemerkenswerte Steigerung der Empfindlichkeit sowie das niedrige Anregungspotential etablieren m-Carboxyluminol als überlegene ECL-Sonde mit Bedeutung für Chemilumineszenz- und enzymatische bioanalytische Anwendungen. [ABSTRACT FROM AUTHOR]

Highly porous laser-induced graphene (LIG) is easily generated in complex electrode configurations such as interdigitated electrodes (IDEs). Here, we demonstrate that their superior capacitive response at low frequencies can be exploited in affinity biosensors using thrombin aptamers as model biorecognition elements. Of specific interest was the effect of electrode surface area on capacitance detection, and the comparison between a label-free format and enhancement strategies afforded by carboxy group bearing polymeric nanoparticles or liposomes. Electrochemical impedance spectroscopy (EIS) was used to investigate the LIG performance and optimize the biosensor design. Interestingly, the label-free strategy performed extremely well and additional labels decreased the limit of detection or increased the sensitivity only minimally. It is assumed that the highly porous nature of the LIG structures dominates the capacitive response so that labels removed from the surface have only limited influence Also, while slight performance changes can be observed for smaller vs. larger electrode structures, the performance of a LIG IDE is reasonably independent of its size. In the end, a dynamic range of 5 orders of magnitude was obtained (0.01 nM–1000 nM) with a limit of detection as low as 0.12 pM. When measured in serum, this increased to 1.3 pM. The good reproducibility (relative standard deviation (RSD), 4.90%) and repeatability (RSD, 2.59%) and good long-term stability (>7 weeks at 4 °C) prove that a LIG-based capacitance sensor is an excellent choice for affinity-based biosensor. The ease-of-production, the simplicity of modification and the superior performance even in a label-free format indicate that LIG-based biosensors should be considered in point-of-care diagnostics in the future. Image 1 • Changes in interfacial capacitance (C int) influenced the overall |Z|, which allowed highly sensitive detection of thrombin on LIG electrodes. • LIG porous electrodes increased the overall sensitivity of the assay with little contributions from nano-labels needed. • The sensor possessed an LOD of 0.12 pM with a dynamic range of 0.01–1000 nM. • Sensors showed excellent performance for selective and sensitive detection of thrombin with good reproducibility (RSD, 4.90%) and repeatability (2.59%). [ABSTRACT FROM AUTHOR]