Target-Cell-Specific Bioorthogonal and Endogenous ATP Control of Signal Amplification for Intracellular MicroRNA Imaging

Catalytic hairpin assembly-based AIEgen/graphene oxide nanocomposite for fluorescence-enhanced and high-precision spatiotemporal imaging of microRNA in living cells

The low abundance, heterogeneous expression, and temporal changes of miRNA in different cellular locations pose significant challenges for both the detection sensitivity of miRNA liquid biopsy and intracellular imaging. In this work, we report an intelligently assembled biosensor based on catalytic hairpin assembly (CHA) and aggregation-induced emission (AIE), named as catalytic hairpin aggregation-induced emission (CHAIE), for the ultrasensitive detection and intracellular imaging of miRNA-155. To achieve such goal, tetraphenylethylene-N3 (TPE-N3) is used as AIE luminogen (AIEgen), while graphene oxide is introduced to quench the fluorescence. When the target miRNA is present, CHA reaction is triggered, causing the AIEgen to self-assemble with the hairpin DNA. This will restrict the intramolecular rotation of the AIEgen and produce a strong AIE fluorescence. Interestingly, CHAIE does not require any enzyme or expensive thermal cycling equipment, and therefore provides a rapid detection. Under optimal conditions, the proposed biosensor can determine miRNA in the concentration range from 2 pM to 200 nM within 30 min, with the detection limit of 0.42 pM. The proposed CHAIE biosensor in this work offers a low background signal and high sensitivity, making it applicable for highly precise spatiotemporal imaging of target miRNA in living cells.

Endogenous mRNA-Driven "One-To-More" Signal Amplification of DNA Probe for Intracellular miR155 Sensing

The detection of specific intracellular microRNAs could be potentially helpful in understanding the underlying mechanisms of cancer metastasis and invasion. MiRNAs are usually present in lower expression levels, especially in early stage of cancer. Here, we proposed a "one-to-more" amplification strategy for miRNA imaging, by virtue of DNA strand displacements with dual-amplification. This approach involves leveraging high-abundance endogenous mRNA as fuel strand to drive cascade reactions between DNA strands for amplification, enabling the monitoring of low-abundance intracellular microRNA155. Notably, in comparison to the traditional "one-to-one" signal triggering mode, our "one-to-more" amplification strategy led to a remarkable 11.8-fold increase in fluorescence signal. Our approach not only demonstrates a high sensitivity and specificity in detecting miR155, but also allows for discrimination of miR155 expression levels in different cell lines. With the advantages of intracellular signal amplification and reduced background signal, this approach holds substantial potential in the early diagnosis of cancer.

Endogenous Enzyme-Driven Amplified DNA Nanocage Probe for Selective and Sensitive Imaging of Mature MicroRNAs in Living Cancer Cells

Selective and sensitive imaging of intracellular mature microRNAs (miRNAs) is of great importance for biological process study and medical diagnostics. However, this goal remains challenging because of the interference of precursor miRNAs (pre-miRNAs) and the low abundance of mature miRNAs. Herein, we develop an endogenous enzyme-driven amplified DNA nanocage probe (Acage) for the selective and sensitive imaging of mature miRNAs in living cells. The Acage consists of a microRNA-responsive probe, an endogenous enzyme-driven fuel strand, and a DNA nanocage framework with an inner cavity. Benefiting from the size selectivity of DNA nanocage, smaller mature miRNAs rather than larger pre-miRNAs are allowed to enter the cavity of DNA nanocage for molecular recognition; thus, Acage can significantly reduce the signal interference of pre-miRNAs. Moreover, with the driving force of an endogenous enzyme apurinic/apyrimidinic endonuclease 1 (APE1) for efficient signal amplification, Acage enables sensitive intracellular miRNA imaging without an additional external intervention. With these features, Acage was successfully applied for intracellular imaging of mature miRNAs during drug treatment. We believe that this strategy provides a promising pathway for better understanding the functions of mature microRNAs in biological processes and medical diagnostics.

Endogenous AND Logic DNA Nanomachine for Highly Specific Cancer Cell Imaging

Intracellular cancer-related biomarker imaging strategy has been used for specific identification of cancer cells, which was of great importance to accurate cancer clinical diagnosis and prognosis studies. Localized DNA circuits with improved sensitivity showed great potential for intracellular biomarkers imaging. However, the ability of localized DNA circuits to specifically image cancer cells is limited by off-site signal leakage associated with a single-biomarker sensing strategy. Herein, we integrated the endogenous enzyme-powered strategy with logic-responsive and localized signal amplifying capability to construct a self-assembled endogenously AND logic DNA nanomachine (EDN) for highly specific cancer cell imaging. When the EDN encountered a cancer cell, the overexpressed DNA repairing enzyme apurinic/apyrimidinic endonuclease 1 (APE1) and miR-21 could synergistically activate a DNA circuit via cascaded localized toehold-mediated strand displacement (TMSD) reactions, resulting in amplified fluorescence resonance energy transfer (FRET) signal. In this strategy, both endogenous APE1 and miR-21, served as two "keys" to activate the AND logic operation in cancer cells to reduce off-tumor signal leakage. Such a multiplied molecular recognition/activation nanomachine as a powerful toolbox realized specific capture and reliable imaging of biomolecules in living cancer cells.

An APE1 gated signal amplified biosensor driven by catalytic hairpin assembly for the specific imaging of microRNA in situ

In situ imaging of microRNA (miRNA) content and distribution is valuable for monitoring tumor progression. However, tumor specific in situ imaging remains a challenge due to low miRNA abundance, lack of biological compatibility, and poor specificity. In this study, we designed a DNA tetrahedral framework complex with hairpins (DTF-HPAP) consisting of an apurinic/apyrimidinic site (AP site) that could be specifically recognized and cleaved by apurinic/apyrimidinic endonuclease 1 (APE1). Efficient and specific in situ imaging of miR-21 in tumors was thus achieved through catalytic hairpin assembly (CHA) reaction. In this study, DTF-HPAP was successfully constructed to trigger the cumulative amplification of fluorescence signal in situ. The specificity, sensitivity and serum stability of DTF-HPAP were verified in vitro, and DTF-HPAP could be easily taken up by cells, acting as a biosensor to detect tumors in mice. Furthermore, we verified the ability of DTF-HPAP to specifically image miR-21 in tumors, and demonstrated its capability for tumor-specific imaging in clinical samples.

Enzyme-Free Dynamic DNA Reaction Networks for On-Demand Bioanalysis and Bioimaging

ConspectusThe pursuit of in-depth studying the nature and law of life activity has been dominating current research fields, ranging from fundamental biological studies to applications that concern synthetic biology, bioanalysis, and clinical diagnosis. Motivated by this intention, the spatiotemporally controlled and in situ analysis of living cells has been a prospective branch by virtue of high-sensitivity imaging of key biomolecules, such as biomarkers. The past decades have attested that deoxyribonucleic acid (DNA), with biocompatibility, programmability, and customizable features, is a competitive biomaterial for constructing high-performance molecular sensing tools. To conquer the complexity of the wide extracellular-intracellular distribution of biomarkers, it is a meaningful breakthrough to explore high-efficiently amplified DNA circuits, which excel at operating complex yet captivating dynamic reaction networks for various bioapplications. In parallel, the multidimensional performance improvements of nucleic acid circuits, including the availability, detection sensitivity, and reliability, are critical parameters for realizing accurate imaging and cell regulation in bioanalysis.In this Account, we summarize our recent work on enzyme-free dynamic DNA reaction networks for bioanalysis from three main aspects: DNA circuitry functional extension of molecular recognition for epigenetic analysis and regulation, DNA circuitry amplification ability improvement for sensitive biomarker detection, and site-specific activation of DNA circuitry systems for reliable and accurate cell imaging. In the first part, we have designed an epigenetically responsive deoxyribozyme (DNAzyme) circuitry system for intracellular imaging and gene regulation, which enriches the possible analyzed species by chemically modifying conventional DNAzyme. For example, an exquisite N6-methyladenine (m6A)-caged DNAzyme was built for achieving the precise FTO (fat mass and obesity-associated protein)-directed gene regulation. In addition, varieties of DNAzyme-based nanoplatforms with self-sufficient cofactor suppliers were assembled, which subdued the speed-limiting hardness of DNAzyme cofactors in live-cell applications. In the second part, we have developed a series of hierarchically assembled DNA circuitry systems to improve the signal transduction ability of traditional DNA circuits. First, the amplification ability of the DNAzyme circuit has been significantly enhanced via several heterogeneously or homogeneously concatenated circuitry models. Furthermore, a feedback reaction pathway was integrated into these concatenated circuits, thus dramatically increasing the amplification efficiency. Second, considering the complex cellular environment, we have simplified the redundancy of multicomponents or reaction procedures of traditional cascaded circuits, relying on the minimal component complexity and merely one modular catalytic reaction, which guaranteed high cell-delivering uniformity while fostering reaction kinetics and analysis reliability. In the third part, we have constructed in-cell-selective endogenous-stimulated DNA circuitry systems via the multiply guaranteed molecular recognitions, which could not only eliminate the signal leakage, but could also retain its on-site and multiplex signal amplification. Based on the site-specific activation strategy, more circuitry availability in cellular scenarios has been acquired for reliable and precise biological sensing and regulation. These enzyme-free dynamic DNA reaction networks demonstrate the purpose-to-concreteness engineering for tailored multimolecule recognition and multiple signal amplification, achieving high-gain signal transduction and high-reliability targeted imaging in bioanalysis. We envision that the enzyme-free dynamic DNA reaction network can contribute to more bioanalytical layouts, which will facilitate the progression of clinical diagnosis and prognosis.

Engineered aptamers for molecular imaging

Molecular imaging, including quantification and molecular interaction studies, plays a crucial role in visualizing and analysing molecular events occurring within cells or organisms, thus facilitating the understanding of biological processes. Moreover, molecular imaging offers promising applications for early disease diagnosis and therapeutic evaluation. Aptamers are oligonucleotides that can recognize targets with a high affinity and specificity by folding themselves into various three-dimensional structures, thus serving as ideal molecular recognition elements in molecular imaging. This review summarizes the commonly employed aptamers in molecular imaging and outlines the prevalent design approaches for their applications. Furthermore, it highlights the successful application of aptamers to a wide range of targets and imaging modalities. Finally, the review concludes with a forward-looking perspective on future advancements in aptamer-based molecular imaging.

Stimuli-responsive probes for amplification-based imaging of miRNAs in living cells

MicroRNAs (miRNAs) have emerged as important biomarkers in biomedicine and bioimaging due to their roles in various physiological and pathological processes. Real-time and in situ monitoring of dynamic fluctuation of miRNAs in living cells is crucial for understanding these processes. However, current miRNA imaging probes still have some limitations, including the lack of effective amplification methods for low abundance miRNAs bioanalysis and uncontrollable activation, leading to background signals and potential false-positive results. Therefore, researchers have been integrating activatable devices with miRNA amplification techniques to design stimuli-responsive nanoprobes for "on-demand" and precise imaging of miRNAs in living cells. In this review, we summarize recent advances of stimuli-responsive probes for the amplification-based imaging of miRNAs in living cells and discuss the future challenges and opportunities in this field, aiming to provide valuable insights for accurate disease diagnosis and monitoring.

Fluorescent Features and Applicable Biosensing of a Core-Shell Ag Nanocluster Shielded by a DNA Tetrahedral Nanocage

The DNA frame structure as a natural shell to stably shield the sequence-templated Ag nanocluster core (csAgNC) is intriguing yet challenging for applicable fluorescence biosensing, for which the elaborate programming of a cluster scaffold inside a DNA-based cage to guide csAgNC nucleation might be crucial. Herein, we report the first design of a symmetric tetrahedral DNA nanocage (TDC) that was self-assembled in a one-pot process using a C-rich csAgNC template strand and four single strands. Inside the as-constructed soft TDC architecture, the template sequence was logically bridged from one side to another, not in the same face, thereby guiding the in situ synthesis of emissive csAgNC. Because of the strong electron-repulsive capability of the negatively charged TDC, the as-formed csAgNC displayed significantly improved fluorescence stability and superb spectral behavior. By incorporating the recognizable modules of targeted microRNAs (miRNAs) in one vertex of the TDC, an updated TDC (uTDC) biosensing platform was established via the photoinduced electron transfer effect between the emissive csAgNC reporter and hemin/G-quadruplex (hG4) conjugate. Because of the target-interrupted csAgNC switching in three states with the spatial proximity and separation to hG4, an "on-off-on" fluorescing signal response was executed, thus achieving a wide linear range to miRNAs and a limit of detection down to picomoles. Without complicated chemical modifications, this simpler and more cost-effective strategy offered accurate cell imaging of miRNAs, further suggesting possible therapeutic applications.

Nanoporous Crystalline Materials for the Recognition and Applications of Nucleic Acids

Nucleic acid plays a crucial role in countless biological processes. Hence, there is great interest in its detection and analysis in various fields from chemistry, biology, to medicine. Nanoporous crystalline materials exhibit enormous potential as an effective platform for nucleic acid recognition and application. These materials have highly ordered and uniform pore structures, as well as adjustable surface chemistry and pore size, making them good carriers for nucleic acid extraction, detection, and delivery. In this review, the latest developments in nanoporous crystalline materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular organic frameworks (SOFs) for nucleic acid recognition and applications are discussed. Different strategies for functionalizing these materials are explored to specifically identify nucleic acid targets. Their applications in selective separation and detection of nucleic acids are highlighted. They can also be used as DNA/RNA sensors, gene delivery agents, host DNAzymes, and in DNA-based computing. Other applications include catalysis, data storage, and biomimetics. The development of novel nanoporous crystalline materials with enhanced biocompatibility has opened up new avenues in the fields of nucleic acid analysis and therapy, paving the way for the development of sensitive, selective, and cost-effective diagnostic and therapeutic tools with widespread applications.

A universal and specific RNA biosensor via DNA circuit-mediated PAM-independent CRISPR/Cas12a and PolyA-rolling circle amplification

Point of care testing (POCT) has important clinical significance for the diagnosis and prognosis evaluation of diseases. At present, the biosensor based on CRISPR/Cas12a has become a powerful diagnostic tool due to its high sensitivity. However, CRISPR/Cas12a requires PAM sequence to recognize target double strand and only can recognize specific sequence, so it is not universal. The current RNA detection techniques either lack consideration for specificity and universality, are expensive and difficult, or both. Therefore, it is crucial to create a CRISPR/Cas12a-based RNA detection system that is easy to use, cheap, specific, and universal in order to further its use in molecular diagnostics. Here, we established a DNA circuit-mediated PAM-independent CRISPR/Cas12a coupled PolyA-rolling circle amplification for RNA detection biosensor, namely DCPRBiosensor. The DCPRBiosensor not only functions as a simple, inexpensive, and highly sensitive RNA detection sensor, but it also boasts innovative specificity and universality features. More importantly, DCPRBiosensor removes the PAM restriction of CRISPR/Cas12a. The DCPRBiosensor's detection limit reached 100 aM and it had a linear relationship between 100 aM and 10 pM. We detected four piRNAs to verify the universality and stability of DCPRBiosensor. Then, we verified that DCPRBiosensor has good discrimination ability for single-base mismatch. Finally, we successfully detected piRNA in DLD-1 and HCT-116 cells and urine mixed samples within 4.5 h. In conclusion, we believe that DCPRBiosensor will have a substantial impact on both the development of CRISPR/as12a's applications and the investigation of the clinical value of piRNA.

Target-catalyzed self-assembled spherical G-quadruplex/hemin DNAzymes for highly sensitive colorimetric detection of microRNA in serum

The accurate and visual detection of circulating microRNA (miRNA) has attracted increasing interest due to its pivotal role in clinical disease diagnosis. Taking advantages of nucleic acid isothermal amplification and enzyme-catalyzed chromogenic reaction, here, a colorimetric sensing strategy was proposed for sensitive miRNA analysis. When the target miRNA was present, local catalytic hairpin assembly (CHA) would be triggered and proceed continuously to form dozens of double-stranded oligonucleotides with G-rich sticky ends on the gold nanoparticle, which could self-assemble into a spherical G-quadruplex (GQ)/hemin DNAzyme by binding with hemin and potassium ions. As a horseradish peroxidase-mimic, GQ/hemin DNAzyme could catalyze the redox reaction and color change of the substrates. Taking miRNA-21 as an example, the developed method exhibited satisfactory specificity as well as high sensitivity with a detection limit of 90.3 fM. Furthermore, the sensing platform has been successfully employed to detect miRNA-21 in spiked serum, providing a promising tool for early diagnosis of cancers.

High-fidelity imaging of intracellular microRNA via a bioorthogonal nanoprobe

The spatiotemporal visualization of intracellular microRNA (miRNA) plays a critical role in the diagnosis and treatment of malignant disease. Although DNAzyme-based biosensing has been regarded as the most promising candidate, inefficient analytical resolution is frequently encountered. Here, we propose a bioorthogonal approach toward high-fidelity imaging of intracellular miRNA by designing a multifunctional nanoprobe that integrates MnO₂ nanosheet-mediated intracellular delivery and activation by a fat mass and obesity-associated protein (FTO)-switched positive feedback. MnO₂ nanosheets facilitate nanoprobe delivery and intracellular DNAzyme cofactors are released upon glutathione-triggered reduction. Meanwhile, an m6A-caged DNAzyme probe could be bioorthogonally activated by intracellular FTO to eliminate potential off-target activation. Therefore, the activated DNAzyme probe and substrate probe could recognize miRNA to perform cascade signal amplification in the initiation of the release of Mn²⁺ from MnO₂ nanosheets. This strategy realized high-fidelity imaging of intracellular aberrant miRNA within tumor cells with a satisfactory detection limit of 9.7 pM, paving the way to facilitate clinical tumor diagnosis and prognosis monitoring.

Metal-Organic Frameworks Nanocarriers for Functional Nucleic Acid Delivery in Biomedical Applications

Metal-organic frameworks (MOFs), a distinctive funtionalmaterials which is constructed by various metal ions and organic molecules, have gradually attracted researchers' attention from they were founded. In the last decade, MOFs emerge as a biomedical material with potential applications due to their unique properties. However, the MOFs performed as nanocarriers for functional nucleic acid delivery in biomedical applications rarely summarized. In this review, we introduce recent developments of MOFs for nucleic acid delivery in various biologically relevant applications, with special emphasis on cancer therapy (including siRNA, ASO, DNAzyme, miRNA and CpG oligodeoxynucleotides), bioimaging, biosensors and separation of biomolecules. We expect the accomplishment of this review could benefit certain researchers in biomedical field to develop novel sophisticated nanocarriers for functional nucleic acid delivery based on the promising material of MOFs.

Dual factor coactivatable fluorescent nanosensor with boosted cytoplasmic biomarker accessibility toward selective tumor imaging

Fluorescent nanosensor-based tumor imaging holds great promise in cancer diagnosis and treatment assistance, yet the signal contrast is heavily hampered by the unspecific/unwanted activation at microscopic regions with a highly restricted local abundance of biomarkers. Herein, we developed an activation boosting strategy by the integration and manipulation of dual-factor coactivation of sensing and lysosome escape facilitated the rise of cytosolic biomarker accessibility. By employing hybrid DNA probes on gold nanoquenchers, ATP sensing initiated conformation switch of the corresponding aptamer units triggered the exposure of a hidden toehold in a loop structure. Sequentially, miRNA-21 sensing was triggered by toehold-mediated strand displacement and detachment of the binding complexes. The application of lysosomotropic agent chloroquine at optimized time interval facilitated the release of nanosensors into the cytosol and a ∼10.5-fold increment of intracellular fluorescence in vitro, while coactivation improved the cancer-to-normal cell signal ratio by ∼5.9 times. The synergy effects led to a high tumor-to-normal tissue ratio value of ∼7.9 in the in vivo imaging results. This strategy establishes a new paradigm of fluorescent nanosensors for selective and specific tumor imaging.

Functionalized photosensitive metal-organic framework as a theranostic nanoplatform for turn-on detection of MicroRNA and photodynamic therapy

Developing a theranostic platform integrating precise diagnostic and efficient treatment is significant but challenging. Here, we reported a new theranostic platform - hairpin probe - photosensitizing MOFs (HPMOF) composed of photosensitizing MOFs (PMOFs) and hairpin probes labeled with fluorophore and quencher, in which PMOF played the role of photosensitizer and nanocarrier of the hairpin probe. The HPMOF was covered with a layer of ZIF-8 to achieve the dual-layered nanotheranostics (HPMOF@ZIF-8). The HPMOF@ZIF-8 achieved high DNA loading capacity and intracellular delivery for tumor-related miRNA imaging. Moreover, HPMOF@ZIF-8 could generate reactive oxygen species with high efficiency, which induced cell apoptosis, leading to efficient photodynamic therapy. Due to the different expression of miRNA between normal cells and cancer cells, the HPMOF@ZIF-8 could recognize cancer cells through imaging of miRNA, leading to more accurate treatment of cancer, providing a promising theranostic nanoplatform.

An Enzymatically Gated Catalytic Hairpin Assembly Delivered by Lipid Nanoparticles for the Tumor-Specific Activation of Signal Amplification in miRNA Imaging

MicroRNA (miRNA) imaging in disease sites is vital to elucidate their role in cancer progression. However, limited tumor specificity remains a major barrier for traditional amplification approaches due to associated background signal leakage. Here, we report a generalizable approach via the combination of enzymatically triggered catalytic hairpin assembly with lipid nanoparticles (LNPs)-based delivery strategy for tumor-specific activation of signal amplification and therefore sensitive miRNA imaging. The signal amplification is established via engineering of traditional catalytic hairpin assembly with enzymatically activated motifs to achieve triggable miRNA imaging in cancer cells. Furthermore, by the introduction of LNPs to combat biological barriers, we demonstrate that the system enables amplified miRNA imaging in vivo with reduced off-tumor signal, leading to enhanced tumor-to-background contrast compared with traditional methods. This approach that relies on specific triggers and controlled delivery to distinguish miRNA in cancer cells from normal cells should be useful in tumor diagnosis.

Dual-Locked DNAzyme Platform for In Vitro and In Vivo Discrimination of Cancer Cells

Imaging of tumor-associated microRNAs (miRNAs) can provide abundant information for cancer diagnosis, whereas the occurrence of trace amounts of miRNAs in normal cells inevitably causes an undesired false-positive signal in the discrimination of cancer cells during miRNA imaging. In this study, we propose a dual-locked (D-locked) platform consisting of the enzyme/miRNA-D-locked DNAzyme sensor and the honeycomb MnO₂ nanosponge (hMNS) nanocarrier for highly specific cancer cell imaging. For a proof-of-concept demonstration, apurinic/apyrimidinic endonuclease 1 (APE1) and miR-21 were chosen as key models. The hMNS nanocarrier can efficiently release the D-locked DNAzyme sensor in living cells due to the decomposition of hMNS by glutathione, which can also supply Mn²⁺ for DNAzyme cleavage. Ascribing to the smart design of the D-locked DNAzyme sensor, the fluorescence signal can only be generated by the synergistic response of APE1 and miR-21 that are overexpressed in cancer cells. Compared with the miRNA single-locked DNAzyme sensor and the small-molecule (ATP)/miRNA D-locked DNAzyme sensor, the proposed enzyme (APE1)/miRNA D-locked DNAzyme sensor exhibited 2.6-fold and 2.4-fold higher discrimination ratio (F_cancer/F_normal) for cancer cell discrimination, respectively. Owing to the superior performance, the D-locked strategy can selectively generate a fluorescence signal in cancer cells, facilitating accurate discrimination of cancer both in vitro and in vivo. Furthermore, this D-locked platform is easily adaptable toward other target molecules by redesigning the DNA sequences. The outstanding performance and expansibility of this D-locked platform holds promising prospects for cancer diagnosis and related biomedical applications.

Recent Progress Toward Imaging Application of Multifunction Sonosensitizers in Sonodynamic Therapy

Sonodynamic therapy (SDT) is a rapidly developing non-surgical therapy that initiates sensitizers’ catalytic reaction using ultrasound, showing great potential for cancer treatment due to its high safety and non-invasive nature. In addition, recent research has found that using different diagnostic and therapeutic methods in tandem can lead to better anticancer outcomes. Therefore, as essential components of SDT, sonosensitizers have been extensively explored to optimize their functions and integrate multiple medical fields. The review is based on five years of articles evaluating the combined use of SDT and imaging in treating cancer. By developing multifunctional sonosensitive particles that combine imaging and sonodynamic therapy, we have integrated diagnosis into the treatment of precision medicine applications, improving SDT cell uptake and antitumor efficacy utilizing different tumour models. This paper describes the imaging principle and the results of cellular and animal imaging of the multifunctional sonosensitizers. Efforts are made in this paper to provide data and design references for future SDT combined imaging research and clinical application development and to provide offer suggestions.

Recent Advances in Near-Infrared-II Fluorescence Imaging for Deep-Tissue Molecular Analysis and Cancer Diagnosis

Fluorescence imaging with high sensitivity and minimal invasiveness has received tremendous attention, which can accomplish visualized monitoring and evaluation of cancer progression. Compared with the conventional first near-infrared (NIR-I) optical window (650-950 nm), fluorescence imaging in the second NIR optical window (NIR-II, 950-1700 nm) exhibits deeper tissue penetration capability and higher temporal-spatial resolution with lower background interference for achieving deep-tissue in vivo imaging and real-time monitoring of cancer development. Encouraged by the significant preponderances, a variety of multifunctional NIR-II fluorophores have been designed and fabricated for sensitively imaging biomarkers in vivo and visualizing the treatment procedure of cancers. In this review, the differences between NIR-I and NIR-II fluorescence imaging are briefly introduced, especially the advantages of NIR-II fluorescence imaging for the real-time visualization of tumors in vivo and cancer diagnosis. An important focus is to summarize the NIR-II fluorescence imaging for deep-tissue biomarker analysis in vivo and tumor tissue visualization, and a brief introduction of NIR-II fluorescence imaging-guided cancer therapy is also presented. Finally, the significant challenges and reasonable prospects of NIR-II fluorescence imaging for cancer diagnosis in clinical applications are outlined.

Dispersion-to-localization of catalytic hairpin assembly for sensitive sensing and imaging microRNAs in living cells from whole blood

Localized DNA circuits have shown good performance regarding reaction rate and sensitivity for sensing intracellular microRNAs (miRNAs). However, these methods reported recently require large kinds of DNA strands and suffer from low signal-to-background (S/B) ratio, which hinder their clinical application. To circumvent these issues, we herein developed a novel strategy for sensitive sensing and imaging miRNAs in living cells based on dispersion-to-localization of catalytic hairpin assembly (DL-CHA). This strategy consists of only three classes of DNA strands (two hairpins and a linker strand), which largely reduces sequence design complexity. Additionally, owing to the unique engineering of the substrate transformation from dispersion to localization, the DL-CHA exhibits not only minimal background leakage but also intensive signal amplification, thus significantly improving the S/B ratio. In particular, the simple sensing method is capable of imaging miRNAs in cells from clinical blood samples for the diagnosis of breast cancer. Therefore, this work provides a powerful tool for intracellular molecules detection and gives a much broader design space for constructing high-performance DNA circuits.

A Redox-Activatable DNA Nanodevice for Spatially-Selective, AND-Gated Imaging of ATP and Glutathione in Mitochondria

Design of biosensors capable of imaging ATP and glutathione (GSH) in mitochondria remains a challenge, despite their importance in elucidating their correlated pathophysiological events. Here, we report a new strategy that uses redox-activatable aptamer sensor design combined with nanoparticle-based targeting capability to achieve spatially controlled, AND-gated imaging of ATP and GSH in mitochondria. The DNA nanodevice was designed by the controlled assembly of the redox-responsive ATP aptamer probe on the nanoparticles and further decorated with mitochondria-targeting signals. We demonstrate that the system allows for mitochondria-specific, correlated imaging of ATP and GSH in living cells and in vivo. Furthermore, because the system can be lighted up only when meeting the "dual keys" (overexpressed ATP and GSH in mitochondria) simultaneously, the DNA nanodevice enables specific imaging of tumors in vivo with improved tumor-to-normal tissue ratio. This work illustrates the potential of the DNA nanodevices in the imaging of mitochondrial multivariate targets.

Bioorthogonal regulation of DNA circuits for smart intracellular microRNA imaging

Catalytic DNA circuits represent a versatile toolbox for tracking intracellular biomarkers yet are constrained with low anti-interference capacity originating from their severe off-site activation. Herein, by introducing an unprecedented endogenous DNA repairing enzyme-powered pre-selection strategy, we develop a sequential and specific on-site activated catalytic DNA circuit for achieving the cancer cell-selective imaging of microRNA with high anti-interference capacity. Initially, the circuitry reactant is firmly caged by an elongated stabilizing duplex segment with a recognition/cleavage site of a cell-specific DNA repairing enzyme, which can prevent undesired signal leakage prior to its exposure to target cells. Then, the intrinsic DNA repairing enzyme of target cells can liberate the DNA probe for efficient intracellular microRNA imaging via the multiply guaranteed molecular recognition/activation procedures. This bioorthogonal regulated DNA circuit presents a modular and programmable amplification strategy for highly reliable assays of intracellular biomarkers, and provides a pivotal molecular toolbox for living systems.

An on-site bioorthogonal regulated DNA circuit was developed by introducing an endogenous DNA repairing enzyme-mediated sequential activation strategy to achieve cancer cell-selective microRNA imaging with high anti-interference ability.

Recent Advances on Functional Nucleic-Acid Biosensors

In the past few decades, biosensors have been gradually developed for the rapid detection and monitoring of human diseases. Recently, functional nucleic-acid (FNA) biosensors have attracted the attention of scholars due to a series of advantages such as high stability and strong specificity, as well as the significant progress they have made in terms of biomedical applications. However, there are few reports that systematically and comprehensively summarize its working principles, classification and application. In this review, we primarily introduce functional modes of biosensors that combine functional nucleic acids with different signal output modes. In addition, the mechanisms of action of several media of the FNA biosensor are introduced. Finally, the practical application and existing problems of FNA sensors are discussed, and the future development directions and application prospects of functional nucleic acid sensors are prospected.

Ultrasensitive and Simultaneous SERS Detection of Multiplex MicroRNA Using Fractal Gold Nanotags for Early Diagnosis and Prognosis of Hepatocellular Carcinoma

Sensitive and simultaneous detection of multiple cancer-related biomarkers in serum is essential for diagnosis, therapy, prognosis, and staging of cancer. Herein, we proposed a magnetically assisted sandwich-type surface-enhanced Raman scattering (SERS)-based biosensor for ultrasensitive and multiplex detection of three hepatocellular carcinoma-related microRNA (miRNA) biomarkers. The biosensor consists of an SERS tag (probe DNA-conjugated DNA-engineered fractal gold nanoparticles, F-AuNPs) and a magnetic capture substrate (capture DNA-conjugated Ag-coated magnetic nanoparticles, AgMNPs). The proposed strategy achieved simultaneous and sensitive detection of three miRNAs (miRNA-122, miRNA-223, and miRNA-21), and the limits of detection of the three miRNAs in human serum are 349 aM for miRNA-122, 374 aM for miRNA-223, and 311 aM for miRNA-21. High selectivity and accuracy of the SERS biosensor were proved by practical analysis in human serum. Moreover, the biosensor exhibited good practicability in multiplex detection of three miRNAs in 92 clinical sera from AFP-negative patients, patients before and after hepatectomy, recurred and relapse-free patients after hepatectomy, and hepatocellular carcinoma patients at distinct Barcelona clinic liver cancer stages. The experiment results demonstrate that our SERS-based assay is a promising candidate in clinical application and exhibited potential for the prediction, diagnosis, monitoring, and staging of cancers.