Monitoring and imaging pH in biofilms utilizing a fluorescent polymeric nanosensor

Abstract

Biofilms are ubiquitous in nature and in the man-made environment. Given their harmful effects on human health, an in-depth understanding of biofilms and the monitoring of their formation and growth are important. Particularly relevant for many metabolic processes and survival strategies of biofilms is their extracellular pH. However, most conventional techniques are not suited for minimally invasive pH measurements of living biofilms. Here, a fluorescent nanosensor is presented for ratiometric measurements of pH in biofilms in the range of pH 4.5–9.5 using confocal laser scanning microscopy. The nanosensor consists of biocompatible polystyrene nanoparticles loaded with pH-inert dye Nile Red and is surface functionalized with a pH-responsive fluorescein dye. Its performance was validated by fluorometrically monitoring the time-dependent changes in pH in E. coli biofilms after glucose inoculation at 37 °C and 4 °C. This revealed a temperature-dependent decrease in pH over a 4-h period caused by the acidifying glucose metabolism of E. coli. These studies demonstrate the applicability of this nanosensor to characterize the chemical microenvironment in biofilms with fluorescence methods.

Dual color pH probes made from silica and polystyrene nanoparticles and their performance in cell studies

“…In the last decades, also an increasing number of modularly built nanoparticle (NP)-based sensors has been reported, utilizing, e.g., silica and polymer NPs, lanthanide-based upconversion NPs, and semiconductor quantum dots in combination with organic sensor dyes 4,19,[39][40][41][42][43][44][45][46] . Nanomaterials which have been the most frequently employed for the preparation of nanosensors for bioimaging applications are organic polymeric particles such as biocompatible polystyrene (PS) NPs (PSNPs), and inorganic silica (SiO 2 ) NPs (SiO 2 -NPs) that can be prepared in a variety of sizes with different surface functionalities [47][48][49][50][51] .…”

“…For core staining, the hydrophobic and neutral dye Nile Red (NR) was chosen as pH-inert reference dye and encapsulated in the polymer matrix by a simple swelling procedure (Fig. 3a 41,57 . The synthesis of the amorphous SiO 2 -NPs of similar size involved multistep hydrolysis and condensation reactions of the silicon precursor in a biphasic cyclohexane/ water system (SI, Fig.…”

Influence of Nanoparticle Encapsulation and Encoding on the Surface Chemistry of Polymer Carrier Beads

“…A change in zeta potential is in good agreement with previous results obtained with dye-loaded polystyrene NPs and MPs using a similar swelling procedure, that also indicated an increase of the zeta potential after the dye-loading of around 10 mV (used dyes/particles: a dyad dye and a rhodamine-B derivate with self-manufactured polystyrene NPs and MPs, as well as NR with commercially available polystyrene NPs). 41,54 To determine the in uence of the QDs on PSMP loading, similar studies were performed with the amphoteric dye RITC and the neutral polarity probe NR using our post-synthetic swelling procedure previously optimized for different classes of organic dyes, 46 see also SI for more details. The resulting RITC-and NR-loaded PSMPs showed zeta potentials of -39 mV and − 40 mV, respectively.…”

Advances in non-invasive biosensing measures to monitor wound healing progression

“…Thus, monitoring pH will provide important data on possible infection in the inflammation phase. pH can be easily measured with the help of indicator dyes (Kromer et al, 2022;Srivastava et al, 2022). However, care must be taken that these dyes do not leach from the dressings.…”