Recent progress in sensing application of metal nanoarchitecture-enhanced fluorescence

Fluorogen-Functionalized Mesoporous Silica Hybrid Sensing Materials: Applications in Cu2+ Detection

Since Cu2+ ions play a pivotal role in both ecosystems and human health, the development of a rapid and sensitive method for Cu2+ detection holds significant importance. Fluorescent mesoporous silica materials (FMSMs) have garnered considerable attention in the realm of chemical sensing, biosensing, and bioimaging due to their distinctive structure and easily functionalized surfaces. As a result, numerous Cu2+ sensors based on FMSMs have been devised and extensively applied in environmental and biological Cu2+ detection over the past few decades. This review centers on the recent advancements in the methodologies for preparing FMSMs, the mechanisms underlying sensing, and the applications of FMSMs-based sensors for Cu2+ detection. Lastly, we present and elucidate pertinent perspectives concerning FMSMs-based Cu2+ sensors.

Microfluidic devices integrated with plasmonic nanostructures for sensitive fluorescent immunoassays

The robust identification and quantification of various biomarkers is of utmost significance in clinical diagnostics and precision medicine. Fluorescent immunoassays are widely used and considered as a gold standard for biomarker detection due to their high specificity and accuracy. However, current commercial immunoassay tests suffer from limited detection sensitivity and complicated, labor-intensive operation procedures, making them impractical for point-of-care diagnosis, particularly in resource-limited regions. Recently, microfluidic immunoassay devices integrated with plasmonic nanostructures have emerged as a powerful tool for sensitive detection of biomarkers, addressing specific issues, such as integration schemes, easy operation, multiplexed detection, and sensitivity enhancement. In this paper, we provide a discussion on the recent advances in the plasmonic nanostructures integrated with microfluidic devices for fluorescent immunoassays. We shed light on the nanofabrication strategies and various fluidic designs for rapid, sensitive, and highly efficient sensing of antigens. Finally, we share our perspectives on the potential directions of these integrated devices for practical applications.

Innovative, Flexible, and Miniaturized Microfluidic Paper-Based Plasmonic Chip for Efficient Near-Infrared Metal Enhanced Fluorescence Biosensing and Imaging

The implementation of metal enhanced fluorescence (MEF) as an efficient detection tool, especially in the near-infrared region of the electromagnetic spectrum, is a rather new direction for diagnostic analytical technologies. In this context, we propose a novel microfluidic plasmonic design based on paper for efficient MEF detection of the "proof-of-concept" biotin-streptavidin recognition interaction. Our design made use of the benefits of gold nanobipyramids (AuBPs), considering the strong enhanced electromagnetic field present at their sharp tips, and filter paper to operate as a natural microfluidic channel due to excellent wicking abilities. The calligraphed plasmonic paper, obtained using a commercial pen filled with AuBPs, was integrated in a robust sandwich optically transparent polydimethylsiloxane chip, exhibiting portability and flexibility while preserving the chip's properties. To place the Alexa 680 fluorophore at an optimal distance from the nanobipyramid substrate, the human IgG-anti-IgG-conjugated biotin sandwich reaction was employed. Thus, upon the capture of Alexa 680-conjugated streptavidin by the biotinylated system, a 1.3-fold average enhancement of the fluorophore's emission was determined by bulk fluorescence measurements. However, the local enhancement factor was considerably higher with values spanning from 5 to 6.3, as proven by mapping the fluorescence emission under both re-scan microscopy and fluorescence lifetime imaging, endorsing the proposed chip's feasibility for bulk MEF biosensing as well as high-resolution MEF bioimaging. Finally, the versatility of our chip was demonstrated by adapting the biosensing protocol for cardiac troponin I biomarker detection, validated using 10 plasma samples collected from pediatric patients and corroborated with a conventional ELISA assay.

Stable Co(II)-based coordination polymer as fluorescence sensor for the discriminative sensing of biomarker methylmalonic acid

Three novel Co-based coordination polymers including {[Co(L)(μ3-O)1/3]2}n (1), {[Co(L)(bimb)]}n (2) and {[Co(L)(bimmb)1/2]}n (3) (H2L = 2,6-di(4-carboxylphenyl)-4-(4-(triazol-1-ylphenyl))pyridine), bimb = 1,4-bis(lmidazol) butane, bimmb = 1,4-bis(imidazole-1-ylmethyl)benzene) were successfully prepared under solvothermal conditions and characterized. Single-crystal X-ray diffraction analyses revealed that 1 possesses a 3D architecture composed of a trinuclear cluster [Co3N3(CO2)6(μ3-O)], 2 exhibits a 2D new topological framework with the point symbol (84·122)(8)2, whereas 3 shows a unique six-fold interpenetrated 3D framework with a (63·82·10)2(63)2(8) topology. Impressively, all of them can function as a highly selective and sensitive fluorescent sensor for the biomarker methylmalonic acid (MMA) via fluorescence quenching. The low detection limit, reusability and high anti-interference performance together make 1-3 become promising sensors for the practical detection of MMA. Furthermore, the successful application of MMA detection in urine sample was demonstrated, which may be a potential candidate for the further development of clinical diagnostic tools.

Aptamer-Based Point-of-Care Devices: Emerging Technologies and Integration of Computational Methods

Recent innovations in point-of-care (POC) diagnostic technologies have paved a critical road for the improved application of biomedicine through the deployment of accurate and affordable programs into resource-scarce settings. The utilization of antibodies as a bio-recognition element in POC devices is currently limited due to obstacles associated with cost and production, impeding its widespread adoption. One promising alternative, on the other hand, is aptamer integration, i.e., short sequences of single-stranded DNA and RNA structures. The advantageous properties of these molecules are as follows: small molecular size, amenability to chemical modification, low- or nonimmunogenic characteristics, and their reproducibility within a short generation time. The utilization of these aforementioned features is critical in developing sensitive and portable POC systems. Furthermore, the deficiencies related to past experimental efforts to improve biosensor schematics, including the design of biorecognition elements, can be tackled with the integration of computational tools. These complementary tools enable the prediction of the reliability and functionality of the molecular structure of aptamers. In this review, we have overviewed the usage of aptamers in the development of novel and portable POC devices, in addition to highlighting the insights that simulations and other computational methods can provide into the use of aptamer modeling for POC integration.

Fluorescence enhancement of organic dyes by femtosecond laser-induced cavitation bubbles for crystal imaging

Fluorescence from organic dyes can be applied in many research fields such as imaging, bio-sensing and diagnosis. One shortcoming of fluorescence imaging is the limitation in emission intensity. Amplification of fluorescence signals can be achieved by the enhancement of localized electromagnetic fields. Metallic nanoparticles are widely applied to produce plasmon resonance, but they cause thermal damage to fragile bio-materials. In this study, we propose a method for nanoparticle-free fluorescence enhancement by ultrafast laser-induced cavitation bubbles in organic dye solutions. Fluorescence enhancement without the use of nanoparticles prevents potential hazards including thermal effects and biotoxicity. In order to achieve fluorescence enhancement in neat dye solution, cavitation bubbles were induced by focusing an 800 nm ultrafast laser beam. Another 400 nm laser beam was used to pump the gain medium. Fluorescence enhancement was observed in various dye solutions. The intensity and spectra of the fluorescence emission can be controlled by changing the power and focus of the excitation laser. According to time-resolved microscopy and simulation results, the cavity formed by the laser-induced bubbles results in the enhancement of the localized electromagnetic field and induces the amplification of the fluorescence signal. The bubble-enhanced fluorescence emission was used for imaging of protein crystals without causing thermal damage to the samples. This study provides an effective method for bio-compatible fluorescence enhancement and has application prospects in fields such as bio-imaging.

Recent advances in plasmon-enhanced luminescence for biosensing and bioimaging

Plasmon-enhanced luminescence (PEL) is a unique photophysical phenomenon in which the interaction between luminescent moieties and metal nanostructures results in a marked luminescence enhancement. PEL offers several advantages and has been extensively used to design robust biosensing platforms for luminescence-based detection and diagnostics applications, as well as for the development of many efficient bioimaging platforms, enabling high-contrast non-invasive real-time optical imaging of biological tissues, cells, and organelles with high spatial and temporal resolution. This review summarizes recent progress in the development of various PEL-based biosensors and bioimaging platforms for diverse biological and biomedical applications. Specifically, we comprehensively assessed rationally designed PEL-based biosensors that can efficiently detect biomarkers (proteins and nucleic acids) in point-of-care tests, highlighting significant improvements in the sensing performance upon the integration of PEL. In addition to discussing the merits and demerits of recently developed PEL-based biosensors on substrates or in solutions, we include a brief discussion on integrating PEL-based biosensing platforms into microfluidic devices as a promising multi-responsive detection method. The review also presents comprehensive details about the recent advances in the development of various PEL-based multi-functional (passive targeting, active targeting, and stimuli-responsive) bioimaging probes, highlighting the scope of future improvements in devising robust PEL-based nanosystems to achieve more effective diagnostic and therapeutic insights by enabling imaging-guided therapy.

Single-Particle Optical Imaging for Ultrasensitive Bioanalysis

The quantitative detection of critical biomolecules and in particular low-abundance biomarkers in biofluids is crucial for early-stage diagnosis and management but remains a challenge largely owing to the insufficient sensitivity of existing ensemble-sensing methods. The single-particle imaging technique has emerged as an important tool to analyze ultralow-abundance biomolecules by engineering and exploiting the distinct physical and chemical property of individual luminescent particles. In this review, we focus and survey the latest advances in single-particle optical imaging (OSPI) for ultrasensitive bioanalysis pertaining to basic biological studies and clinical applications. We first introduce state-of-the-art OSPI techniques, including fluorescence, surface-enhanced Raman scattering, electrochemiluminescence, and dark-field scattering, with emphasis on the contributions of various metal and nonmetal nano-labels to the improvement of the signal-to-noise ratio. During the discussion of individual techniques, we also highlight their applications in spatial-temporal measurement of key biomarkers such as proteins, nucleic acids and extracellular vesicles with single-entity sensitivity. To that end, we discuss the current challenges and prospective trends of single-particle optical-imaging-based bioanalysis.

Optical and topographic characteristics of silver films deposited from a colloidal solution on polyelectrolytes for IgG-FITC fluorescence analysis

The optimization of the fluorescence enhancement factor of the IgG-FITC conjugate as an immunofluorescent marker, depending on the optical and topographic parameters of the colloidal silver film on the surface of a polystyrene plate for immunoassay, was carried out for the first time, and the factors effecting the enhancement were identified. By means of time-resolved spectroscopy as well as by detection the relative concentrations of IgG-FITC adsorbed on the solid phase with enzyme-linked immunoassay, it was shown that fluorescence enhancement in the presence of silver nanoparticles is a resonance process associated with plasmon effects. The most important parameters correlating with the fluorescence enhancement factor are the optical density value at the wavelength of excitation and emission of the fluorophore. The maximum enhancement factor of 10.2 times was obtained for Ag films with the highest optical density.

Advances in Noble-Metal Nanoparticle-Based Fluorescence Detection of Organophosphorus Chemical Warfare Agents

Efficient and simple detection of chemical warfare agents (CWAs) is an essential step in minimizing the potentially lethal consequences of chemical weapons. CWAs are a family of organic chemicals that are used as chemical weapons because of their enormous severity and lethal effects when faced with unforeseen challenges. To stop the spread of CWAs, it is critical to develop a platform that detects them in a sensitive, timely, selective, and minimally invasive manner. Rapid advances in the demand for on-site sensors, metal nanoparticles, and biomarker identification for CWAs have made it possible to use fluorescence as a precise real-time and point-of-care (POCT) testing technique. For POCT-based applications, the new capabilities of micro- and nanomotors offer enormous prospects. In recent decades, significant progress has been made in the design of fluorescent sensors and the further development of noble metal nanoparticles for the detection of organophosphorus CWAs, as described in this review. Through this work, recent attempts to fabricate sensors that can detect organophosphorus CWAs through changes in their fluorescence properties have been summarized. Finally, an integrated outlook on how noble metal nanoparticles could be used to develop smart sensors for organophosphorus CWAs that communicate with and control electronic devices to monitor and improve the health of individuals.

Orhan O, Daly S, O’Regan DD, Rodriguez BJ, Casey E, Rice JH. Electric Field Tunability of Photoluminescence from a Hybrid Peptide-Plasmonic Metal Microfabricated Chip

Enhancement of fluorescence through the application of plasmonic metal nanostructures has gained substantial research attention due to the widespread use of fluorescence-based measurements and devices. Using a microfabricated plasmonic silver nanoparticle-organic semiconductor platform, we show experimentally the enhancement of fluorescence intensity achieved through electro-optical synergy. Fluorophores located sufficiently near silver nanoparticles are combined with diphenylalanine nanotubes (FFNTs) and subjected to a DC electric field. It is proposed that the enhancement of the fluorescence signal arises from the application of the electric field along the length of the FFNTs, which stimulates the pairing of low-energy electrons in the FFNTs with the silver nanoparticles, enabling charge transport across the metal-semiconductor template that enhances the electromagnetic field of the plasmonic nanoparticles. Many-body perturbation theory calculations indicate that, furthermore, the charging of silver may enhance its plasmonic performance intrinsically at particular wavelengths, through band-structure effects. These studies demonstrate for the first time that field-activated plasmonic hybrid platforms can improve fluorescence-based detection beyond using plasmonic nanoparticles alone. In order to widen the use of this hybrid platform, we have applied it to enhance fluorescence from bovine serum albumin and Pseudomonas fluorescens. Significant enhancement in fluorescence intensity was observed from both. The results obtained can provide a reference to be used in the development of biochemical sensors based on surface-enhanced fluorescence.