Excited-State Conjugation/De-Conjugation Driven Nonradiative Thermal Deactivation for Developing Fluorogenic Probes to Diagnose Cancers

Sep 21, 2026

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Fluorogenic probes enable imaging of biological species and diagnosis of diseases, particularly cancers, yet their fluorogenic behavior has been largely limited to a small set of photophysical processes such as PeT, FRET, and ICT. Using calculations and experiments, this work establishes that suppressing excited-state π-conjugation in meso-ester Si-rhodamine SiR-COOM or promoting de-π-conjugation in meso-ester cyanine 5 Cy5-COOM via an “ester-tocarboxylate” conversion can serve as a general fluorogenic mechanism. Based on this mechanism, three Cy5-COOM-derived probes detect cancer biomarkers aminopeptidase N, γ-glutamyltranspeptidase, and nitroreductase, achieving high tumor-to-normal tissue ratios.

LanguageEnglish

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Abstract

Introduction

Fluorogenic Mechanisms and Design Considerations

Substituent-Driven π-Conjugation Effects

ACS Partner Journal This article is licensed under CC-BY-NC-ND 4.0 [pubs.acs.org/ChemBioImaging](pubs.acs.org/ChemBioImaging) Article Excited-State Conjugation/De-Conjugation Driven Nonradiative Thermal Deactivation for Developing Fluorogenic Probes to Diagnose Cancers Hongxing Zhang, Guanlin Lao, Mengxing Liu, Zhihui Jia, Jing Liu, * and Wei Guo* Cite This: Chem. Biomed. Imaging 2024, 2, 432−441 Read Online | | | | | | | | --- | --- | --- | --- | --- | --- | | ACCESS | Metrics & More | | Article Recommendations | | *sı Supporting Information | ABSTRACT: Fluorogenic probes have shown great potential in imaging biological species as well as in diagnosing diseases, especially cancers. However, the fluorogenic mechanisms are largely limited to a few photophysical processes to date, typically including photoinduced electron transfer (PeT), fluorescence resonant energy transfer (FRET), and intramolecular charge transfer (ICT). Herein, by calculations and experiments, we set forth that the inhibition of the excited-state π-conjugation in meso-ester Si-rhodamine SiR-COOM or the de-π-conjugation in meso-ester cyanine 5 Cy5-COOM via the “ester-tocarboxylate” conversion can operate as a general fluorogenic mechanism to fabricate fluorogenic probes. Based on the mechanism and considering the higher chemical stability of Cy5-COOM than that of SiR-COOM, we developed, as a proof-of-concept, three fluorogenic probes Cy5-APN, Cy5-GGT, and Cy5-NTR on the basis of the Cy5-COOM platform for sensing cancer biomarkers aminopeptidase N (APN), γ-glutamyltranspeptidase (GGT), and nitroreductase (NTR), respectively, and demonstrated their outstanding performances in distinguishing between cancerous and normal tissues with the high tumor-tonormal tissue ratios in the range of 9−14. KEYWORDS: Fluorogenic Probes, Cyanine 5, Si-rhodamine, Excited-State, Conjugation, De-Conjugation, Cancer Biomarkers ■ INTRODUCTION Fluorogenic probes as a nonionizing radiation method are among the most powerful cellular biology tools due to their notable merits of cell permeability, visualization, noninvasiveness, high spatiotemporal resolution, and real-time and in situ monitoring, by which imaging of various biological species and dynamic biological events in cells, tissues, and whole organisms could be achieved. 1−5 To fabricate fluorogenic probes to efficiently achieve the above purposes, two critical factors should be taken into account in advance: one is the choice of a fluorophore, characterized by visible-to-near-infrared excitation and emission wavelengths, high fluorescence brightness, and long-term photostability for improving spatiotemporal resolution; and the other is the identification of a fluorogenic mechanism to ensure a large fluorescence off−on response upon interaction with target biological substrates. After decades of efforts, a great variety of fluorophores suitable for bioimaging applications have been exploited, typically including boron dipyrromethenes (BODIPY),6−8 rhodamines (such as O-rhodamines and Si-rhodamines),9−11 and cyanines (such as Cy5 and Cy7);12−14 moreover, considerable success has been achieved in further improving their photophysical performances to meet the increasing requirements of various emerging cutting-edge fluorescence technologies. 15−28 By © 2024 The Authors. Co-published by Nanjing University and American Chemical Society 432 comparison, the reported fluorogenic mechanisms are largely limited to a few photophysical processes, representatively including photoinduced electron transfer (PeT), fluorescence resonant energy transfer (FRET), and intramolecular charge transfer (ICT).29−32 Although effective in most cases, these mechanisms are not without drawback. For instance, the PeT process is solvent polarity- and emission wavelength-dependent, and nonpolar environments or near-infrared excitation/ emission wavelengths often contribute to low or even negligible PeT efficiency.33,34

FAQs

What photophysical mechanisms have traditionally limited fluorogenic probe behavior?

Reported fluorogenic mechanisms have mainly relied on processes such as photoinduced electron transfer (PeT), fluorescence resonant energy transfer (FRET), and intramolecular charge transfer (ICT).

What fluorogenic mechanism is proposed in this study?

The study proposes that inhibiting excited-state π-conjugation in Si-rhodamine meso-ester SiR-COOM, or inducing de-π-conjugation in meso-ester cyanine 5 Cy5-COOM through an “ester-tocarboxylate” conversion, can function as a general fluorogenic mechanism.

Which cancer biomarkers do the developed probes target and how effective are they?

Three probes, Cy5-APN, Cy5-GGT, and Cy5-NTR, sense aminopeptidase N, γ-glutamyltranspeptidase, and nitroreductase, respectively, and distinguish cancerous from normal tissues with tumor-to-normal tissue ratios of about 9–14.

Sep 21, 2026

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