Plasmonic Elastic Capsules as Colorimetric Reversible pH‐Microsensors

Abstract

There is a crucial need for effective and easily dispersible colloidal microsensors able to detect local pH changes before irreversible damages caused by demineralization, corrosion, or biofilms occur. One class of such microsensors is based on molecular dyes encapsulated or dispersed either in polymer matrices or in liquid systems exhibiting different colors upon pH variations. They are efficient but often rely on sophisticated and costly syntheses, and present significant risks of leakage and photobleaching damages, which is detrimental for mainstream applications. Another approach consists of exploiting the distance‐dependent plasmonic properties of metallic nanoparticles. Still, assembling nanoparticles into dispersible colloidal pH‐sensitive sensors remains a challenge. Here, it is shown how to combine optically active plasmonic gold nanoparticles and pH‐responsive thin shells into “plasmocapsules.” Upon pH change, plasmocapsules swell or shrink. Concomitantly, the distance between the gold nanoparticles embedded in the polymeric matrix varies, resulting in an unambiguous color change. Billions of micron‐size sensors can thus be easily fabricated. They are nonintrusive, reusable, and sense local pH changes. Each plasmocapsule is an independent reversible microsensor over a large pH range. Finally, their potential use for the detection of bacterial growth is demonstrated, thus proving that plasmocapsules are a new class of sensing materials.

Tunable Plasmonic Microcapsules with Embedded Noble Metal Nanoparticles for Optical Microsensing

“…13,14 With the development of preparation methods and nanoparticles, the application range has extended to other applications in optics as strong absorbers, 15 in catalysis, 16,17 in biomedical engineering for photo acoustic imaging and photo thermal therapy 18 and in mechanical and chemical sensing (Figure 1). [19][20][21][22] Lately, an increasing research interest has been dedicated to the integration of several types of nanoparticles into multi-functional colloidosomes or MCs. Despite the interest of the scientific community, only few examples of this new type of supracolloidal object have so far been reported.…”

“…Initially, the intended primary use of these new structures was the encapsulation and the controlled release of active ingredients. , With the development of preparation methods and NPs, the application range has extended to other applications in optics as strong absorbers, in catalysis, , in biomedical engineering for photo acoustic imaging and photo thermal therapy, and in mechanical and chemical sensing (Figure ). − …”

Physical mechanisms driving the reversible aggregation of Staphylococcus aureus and response to antimicrobials

“…This result is in agreement with previous reports 6 suggesting that bacterial aggregation provides a microenvironment in which innermost cells are protected from antimicrobial agents. Interestingly, S. aureus is known to acidify its extracellular medium as it multiplies in a closed batch system 26 . Moreover, S. aureus is often www.nature.com/scientificreports/ found on host skin 7 which displays a slightly acidic pH when intact.…”

Nanocrystal Superparticles with Whispering-Gallery Modes Tunable through Chemical and Optical Triggers

“…For instance, microring resonators fabricated using semiconductor nanocrystals (NCs) allow active color control of lasing modes across the visible range . Coupling NCs to microstructures also benefits sensing: silica microspheres coated with plasmonic NCs function as strain and pH sensors, , with an optical response tunable by varying NC composition …”

“…For instance, microring resonators fabricated using semiconductor nanocrystals (NCs) allow active color control of lasing modes across the visible range. NCs to microstructures also benefits sensing: silica microspheres coated with plasmonic NCs function as strain and pH sensors, 32,33 with an optical response tunable by varying NC composition. 34 Recently, the observation that NCs can spontaneously assemble to form photonic structures has encouraged their use as building blocks for photonics.…”