Intracellular Signal Amplification for Ultrasensitive Detection and Imaging: Progress, Challenges, and Opportunities

Abstract

Disease signaling molecules and biomarkers are important in biosensing and biomedicine, and their ultra‐sensitive detection and imaging are critical in medical diagnosis. However, most biomarkers have low levels of expression in cells and are easily degraded; therefore, they cannot be accurately detected in real time by conventional amplification methods, which are typically confined to cell lysates. To achieve highly sensitive detection of intracellular low‐abundance molecules, extensive efforts have been devoted to the development of in situ signal amplification techniques. This review tracks the development of recent advances in in situ signal amplification strategies, and systematically summarizes the advantages and disadvantages of enzymatic and non‐enzymatic amplification techniques for detecting and tracing intracellular targets. Further, perspectives, challenges, and opportunities for intracellular signal amplification are discussed to promote its adoption for in situ signal amplification in clinical settings and to provide new insights into signaling molecules and biomarkers in cellular functions and associated diseases.

Activity-Independent Enzyme-Powered Amplification for Improving Signal Stability and Fidelity in Biosensing

“…Achieving the implementation of signal amplification in living cells with endogenous enzymes is a biofriendly method for low-abundance biological-target detection. 1 For instance, utilizing endogenous β-galactosidase as an amplification enzyme to hydrolyze fluorescent substrates, the amplified fluorescent signal was acquired for in-flow cytometric detection of antigen proteins. 2 Apparently, this enzyme-based signalamplified method was dependent on catalytic capacities of the enzyme; however, the enzymatic activity is easily affected by microenvironment change (e.g., pH and temperature) in a complex cellular microenvironment, 3 causing an unstable or false-positive signal for detection.…”

“…Achieving the implementation of signal amplification in living cells with endogenous enzymes is a biofriendly method for low-abundance biological-target detection . For instance, utilizing endogenous β-galactosidase as an amplification enzyme to hydrolyze fluorescent substrates, the amplified fluorescent signal was acquired for in-flow cytometric detection of antigen proteins .…”