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Metal surfaces can alter the luminescence emitted by nanoparticles through a variety of effects including quenching, plasmonic enhancement, and optical interference-, reflection-, and absorption-related phenomena. While many of these effects are well-established, multiple such effects typically occur in parallel in realistic measurement scenarios, making the relative importance of each effect difficult to discern. As imaging and sensing applications in which luminescent nanoparticles are placed on metal surfaces continue to grow, a detailed understanding of how metal surfaces modify nanoparticle luminescence is increasingly important for optimizing and ensuring correct interpretation of the measurement results. Here, we systematically investigate how metal surfaces affect the luminescence emitted by individual NaYF4:Yb3+,Er3+ upconverting nanoparticles (UCNPs) ∼27 nm in diameter using a judiciously selected set of five different metal coatings with varying optical and thermal properties. We find that the average single-UCNP emission intensity is determined by an interplay between quenching and reflection effects. Consequently, the average single-UCNP emission intensity is correlated with the reflectance of the underlying metal coating, but non-radiative decay rate changes also play an important role, leading to different average single-UCNP emission intensities for metal coatings with near-identical reflectances. We also evaluate metal surface effects on the common ratiometric thermometry signal of NaYF4:Yb3+,Er3+ UCNPs and find that the intrinsic temperature dependence of the luminescence intensity ratio is unaffected by the underlying material. The only differences observed are the result of laser-induced heating for sufficiently absorbing metal coatings on low thermal conductivity substrates, in accordance with the predictions of an analytical heat transfer model.
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NIR Biosensing of Neurotransmitters in Stem Cell‐Derived Neural Interface Using Advanced Core–Shell Upconversion Nanoparticles
Abstract Nondestructive neurotransmitter detection and real‐time monitoring of stem cell differentiation are both of great significance in the field of neurodegenerative disease and regenerative medicine. Although luminescent biosensing nanoprobes have been developed to address this need, they have intrinsic limitations such as autofluorescence, scattering, and phototoxicity. Upconversion nanoparticles (UCNPs) have gained increasing attention for various biomedical applications due to their high photostability, low auto‐fluorescent background, and deep tissue penetration; however, UCNPs also suffer from low emission intensities due to undesirable energy migration pathways. To address the aforementioned issue, a single‐crystal core–shell–shell “sandwich” structured UCNP is developed that is designed to minimize deleterious energy back‐transfer to yield bright visible emissions using low power density excitations. These UCNPs show a remarkable enhancement of luminescent output relative to conventional β‐NaYF4:Yb,Er codoped UCNPs and β‐NaYF4:Yb,Er@NaYF4:Yb “active shell” alike. Moreover, this advanced core–shell–shell UCNP is subsequently used to develop a highly sensitive biosensor for the ultrasensitive detection of dopamine released from stem cell‐derived dopaminergic‐neurons. Given the challenges of in situ detection of neurotransmitters, the developed NIR‐based biosensing of neurotransmitters in stem cell‐derived neural interfaces present a unique tool for investigating single‐cell mechanisms associated with dopamine, or other neurotransmitters, and their roles in neurological processes.
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- PAR ID:
- 10461599
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 31
- Issue:
- 14
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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