ConspectusPrecision medicine is transforming healthcare by enabling stratified and personalized treatments driven by our growing ability to comprehensively characterize molecular features in diseased tissues and liquid biopsies. Advances in genomic, transcriptomic, proteomic, and metabolomic profiling have increasingly reshaped disease diagnostics, shifting monitoring paradigms from a small number of single-analyte biomarkers toward highly multiplexed platforms capable of capturing biological complexity at the systems level. For liquid biopsy profiling in particular, suspension arrays have emerged as a powerful approach for broad biomarker coverage, leveraging "barcode"-based identification to achieve exponentially scalable multiplexing from a limited set of barcoding units. Since the early 1980s, suspension array technologies have evolved within flow cytometry frameworks, accompanied by continuous innovation in optical barcoding architectures. However, optical barcoding remains fundamentally challenged by constrained color palettes and spectral cross-talk, imposing a multiplexing ceiling that restricts barcoding scalability.The multiplexing challenge imposed by optical barcoding has been substantially alleviated by the emergence of metal-isotopic barcoding strategies coupled with inductively coupled plasma mass spectrometry (ICP-MS). Rather than encoding analytes using spectrally overlapping fluorophores, metal barcoding encodes sample identities using combinatorial patterns of multiple nonradioactive metal isotopes with distinct atomic masses, enabling intrinsically orthogonal detection with minimal crosstalk and allowing a far greater number of analytes to be quantified simultaneously within a single assay. Within this class of technologies, mass cytometry, a specialized ICP-MS platform optimized for single-cell (single-particle) analysis, can resolve up to 135 mass channels with high precision, more than 60 of which can be technically used as molecular tags or barcoding channels. Such capability has paved the way for highly scalable suspension array technologies. Despite these advances, two critical challenges still remain: (1) the absence of templated and scalable barcode frameworks that enable rapid and reproducible construction of high-capacity barcode libraries and (2) the need to amplify the biomarker reporter signals to maximize assay sensitivity without compromising barcoding fidelity.To address these challenges, our group has pursued long-term research since 2010 on metal nanoparticle tagging to enhance both the sensitivity and multiplexing capability in pooled-sample bioassays. We began this effort with an early demonstration of metal nanoparticles as "signal amplifiers" in ICP-based mass spectrometry. Beyond sustained efforts in signal enhancement using metal nanotags, our more recent work on a barcoding strategy by controllable nanoparticle accumulation and self-assembly has notably rekindled interest in facile and scalable barcode designs for customizable mass cytometric suspension platforms. Herein, we provide an evolution account of cytometric suspension array and highlight key breakthroughs in scalability by metal-isotopic barcoding. We summarize the mechanism, design considerations, and emerging applications of these barcoding strategies in high-throughput bioassays. Particular emphasis is placed on our conceptual framework, recent advances, and ongoing progress in metal nanoparticle tagging to break through a sensitive bioassay and programmable barcoding for new suspension arrays. We envision that the barcoding strategies iterating from optical to mass cytometry could profoundly reshape biological discovery, multiplexing capacity, and clinical diagnostics, further opening the postfluorescence era for ultrasensitive and high-throughput precision medicine.
Huang et al. (Fri,) studied this question.