This review focuses on metal enhanced fluorescence (MEF) and its current and future applications in biotechnology. The mechanisms of MEF are discussed in terms of the additional radiative and nonradiative decay rates caused by the close proximity of the metal. We then review the current MEF materials and structures that show promise in bioapplications. The use of electromagnetic modelling to predict fluorescent rate enhancement is then considered. We then give particular focus to the recent work carried out in the homogeneous fabrication of metal nanoparticles using colloidal lithography. It is concluded that the use of computational electromagnetic modelling alongside homogeneous fabrication techniques will lead to predictable and controllable MEF, paving the way for increased applications in biotechnology.

To increase disease survival rates, there is a vital need for diagnosis at very preliminary stages.

The rational construction of efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is critical to seawater electrolysis. Herein, trimetallic heterostructured core-shell nanoboxes based on Prussian blue analogues (Ni-Co@Fe-Co PBA) were synthesized using an iterative coprecipitation strategy. The same coprecipitation procedure was used for the preparation of the PBA core and shell, with the synthesis of the shell involving chemical etching during the introduction of ferrous ions. Due to its unique structure and composition, the optimized trimetallic Ni-Co@Fe-Co PBA possesses more active interfacial sites and a high specific surface area. As a result, the developed Ni-Co@Fe-Co PBA electrocatalyst exhibits remarkable electrocatalytic HER performance with small overpotentials of 43 and 183 mV to drive a current density of 10 mA cm^-2 in alkaline freshwater and simulated seawater, respectively. Operando Raman spectroscopy demonstrates the evolution of Co²⁺ from Co³⁺ in the catalyst during HER. Density functional theory simulations reveal that the H*-N adsorption sites lower the barrier energy of the rate-limiting step, and the introduced Fe species improve the electron mobility of Ni-Co@Fe-Co PBA. The charge transfer at the core-shell interface leads to the generation of H* intermediates, thereby enhancing the HER activity. By pairing this HER catalyst (Ni-Co@Fe-Co PBA) with another core-shell PBA OER catalyst (NiCo@A-NiCo-PBA-AA) reported by our group, the fabricated two-electrode electrolyzer was found to achieve high output current densities of 44 and 30 mA cm^-2 at a low voltage of 1.6 V in alkaline freshwater and simulated seawater, respectively, exhibiting remarkable durability over a 100 h test.

We discuss the phenomenon of enhanced fluorescence in the proximity of metal nanostructures addressing the question of how much fluorescence signal can be obtained from fluorophores in such altered environments. We review its applicability for the methodologies used in the life science, such as immunoassays, flow cytometry and bioimaging. Experimental and theoretical scenarios employing various metal nanostructures – such as homogeneous enhancing substrates, fluorescence-enhancing microbeads, and metal core–dielectric shell nanocomposites – are described.

Gold nanostars (AuNSs) are receiving increasing attention for their potential applications in bionanotechnology because of their unique optical properties related to their complex branched morphology. Their sharp features allow strong localized surface plasmon resonances, tunable in the near-infrared (NIR) region, and large enhancements of local electromagnetic fields. Here, the application of AuNSs in metal-enhanced fluorescence (MEF) in the NIR and second NIR (NIR-II) biological windows is explored for the first time. NIR/NIR-II fluorophores are incorporated onto monolayers of AuNSs with tunable plasmonic responses. Over 320-fold fluorescence enhancement is achieved in the NIR, confirming that AuNS substrates are promising NIR-MEF platforms for the development of ultrasensitive biosensing applications. Using fluorescence lifetime measurements to semiquantitatively deconvolute the excitation enhancement from emission enhancement, as well as modeling to simulate the electric field enhancement, we show that a combination of enhanced excitation and an increased radiative decay rate, accompanied by an increase in the quantum yield, contribute to the observed large enhancement. AuNSs with different morphological features exhibit significantly different excitation enhancements, indicating the important role of the particle morphology on the magnitude of electromagnetic field enhancement and the resulting enhancement factor. Importantly, enhancement factors of up to 50-fold are also achieved in the NIR-II region, suggesting that this system holds promise for the future development of bright probes for NIR/NIR-II biosensing and bioimaging.