ConspectusFluorescent molecular sensors, often referred
to as “turn-on”
or “turn-off” fluorescent probes, are synthetic agents
that change their fluorescence signal in response to analyte binding.
Although these sensors have become powerful analytical tools in a
wide range of research fields, they are generally limited to detecting
only one or a few analytes. Pattern-generating fluorescent probes,
which can generate unique identification (ID) fingerprints for different
analytes, have recently emerged as a new class of luminescent sensors
that can address this limitation. A unique characteristic of these
probes, termed ID-probes, is that they integrate the qualities of
conventional small-molecule-based fluorescent sensors and cross-reactive
sensor arrays (often referred to as chemical, optical, or electronic
noses/tongues). On the one hand, ID-probes can discriminate between
various analytes and their combinations, akin to array-based analytical
devices. On the other hand, their minute size enables them to analyze
small-volume samples, track dynamic changes in a single solution,
and operate in the microscopic world, which the macroscopic arrays
cannot access.Here, we describe the principles underlying the
ID-probe technology,
as well as provide an overview of different ID-probes that have been
developed to date and the ways they can be applied to a wide range
of research fields. We describe, for example, ID-probes that can identify
combinations of protein biomarkers in biofluids and in living cells,
screen for several protein inhibitors simultaneously, analyze the
content of Aβ aggregates, as well as ensure the quality of small-molecule
and biological drugs. These examples highlight the relevance of this
technology to medical diagnosis, bioassay development, cell and chemical
biology, and pharmaceutical quality assurance, among others. ID-probes
that can authorize users and protect secret data are also presented
and the mechanisms that enable them to hide (steganography), encrypt
(cryptography), and prevent access to (password protection) information
are discussed.The versatility of this technology is further
demonstrated by describing
two types of probes: unimolecular ID-probes and self-assembled ID-probes.
Probes from the first type can operate inside living cells, be recycled,
and their initial patterns can be more easily obtained in a reproducible
manner. The second type of probes can be readily modified and optimized,
allowing one to prepare various different probes from a much wider
range of fluorescent reporters and supramolecular recognition elements.
Taken together, these developments indicate that the ID-probe sensing
methodology is generally applicable, and that such probes can better
characterize analyte mixtures or process chemically encoded information
than can the conventional fluorescent molecular sensors. We therefore
hope that this review will inspire the development of new types of
pattern-generating probes, which would extend the fluorescence molecular
toolbox currently used in the analytical sciences.