Simple Self-Referenced Luminescent pH Sensors Based on Upconversion Nanocrystals and pH-Sensitive Fluorescent BODIPY Dyes

Abstract

Optical probes for monitoring, imaging, and sensing of pH are of great interest for the scientific community as pH is a crucial marker for many processes in biotechnology, biology, medical diagnostics, biomedical research, and material corrosion. Thereby, optical pH sensors based on fluorescence have attracted interest in particular as fluorescence offers a high sensitivity down to the single molecule level, can be read out with relatively simple and readily miniaturized instrumentation, and allows online in situ measurements. Also the versatility ranging from molecular and nanosensor formats to planar optodes and fiber-optic sensors, and the non-invasive, non-destructive, and contactless nature of the measurement are application-friendly features. The information content, which is offered by a fluorescence intensity-based sensor, is usually unspecific and limited on the presence or the absence of the chromophore or analyte and can additionally be hampered by fluctuation of the excitation light intensity and changes in fluorophore concentration, e.g., due to photobleaching. Therefore, many fluorescence sensors are utilized in referenced systems, which enable twowavelength ratiometric measurements of the fluorescence intensity by the introduction of an analyte-inert reference with a spectrally distinguishable emission. This work presents the rational design of a versatile, modular, multi-component-based platform for ratiometric optical analyte sensing that can be simply adapted to different formats and measurement geometries. Therefore, readily available analyte-responsive fluorescent boron-dipyrromethene (BODIPY) dyes and near infrared (NIR)-excitable multicolour-Partikelgrößen wurden dafür via Transmissionselektronenmikroskopie (TEM) und Kleinwinkel-Röntgenstreuung (SAXS) bestimmt. Neben der Partikelgröße konnten durch die TEM-Messungen auch Informationen über die Kristallphasen der Nanopartikel erhalten werden. Neben der Erfassung des Partikelwachstums wurde die UCL der UCNPs für die ratiometrische Sensorplattform als Nanolampe und gleichzeitig als Referenzsignal verwendet. Die blaue Upconversion(UC)-Emission der NaYF 4 :Yb 3+ /Tm 3+ UCNPs wurde dabei zur Anregung der pH-sensitiven BODIPY-Farbstoffe verwendet, während die rote UC-Emission als inertes Referenzsignal verwendet wurde. Die Berechnung des Verhältnisses der Emissionsintensitäten der grünen Fluoreszenz des Farbstoffs und der roten UC-Emission des Partikels ermöglicht eine Bestimmung des pH-Werts. Das Potenzial dieser Strategie zur Erfassung des pH-Werts wurde beispielhaft für die Bestimmung der zeitabhängigen Änderungen des pH-Werts einer metabolisierenden Escherichia coli (E. coli)-Suspension gezeigt.

Synthesis and spectroscopic characterization of a fluorescent phenanthrene-rhodamine dyad for ratiometric measurements of acid pH values

“…60 Furthermore, the dye can also be integrated into a D4 hydrogel yielding a pH-responsive sensor film as previously done for water-insoluble BODIPY dyes. 52…”

Photoluminescent Nanomaterials for Medical Biotechnology

“…As in the case of other nanomaterials, reliable and stable procedures for UCNP preparation, modification, and functionalization are required, as well as a study of the possible negative consequences of their application [ 183 , 185 , 192 , 193 ]. Despite this, a lot of evidence has been accumulated showing that UCNPs can be successfully applied in the development of agents for optical and multimodal imaging [ 194 , 195 ], sensors [ 196 , 197 ], as well as for photodynamic and photothermal therapy [ 198 , 199 ].…”

Preparation and properties of a novel polystyrene solid-phase fluorescence pH sensor based on a naphthalimide derivative

“…7,8 In recent years, more and more chemical fluorescence sensors have been developed to detect pH due to their high sensitivity and rapid response. [9][10][11][12] However, most of them cannot be reused. Thus, the development of recyclable solid-phase pH sensors is of significant importance for practical applications.…”