Rapid Glutathione Analysis with SERS Microneedles for Deep Glioblastoma Tissue Differentiation.

Rapid tissue differentiation at the molecular level is a prerequisite for precise surgical resection, which is of special value for the treatment of malignant tumors, such as glioblastoma (GBM). Herein, a SERS-active microneedle is prepared by modifying glutathione (GSH)-responsive molecules, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), on the surface of Au@Ag substrates for the distinction of different GBM tissues. Since the Raman signals on the surface of the DTNB@Au@Ag microneedle can be collected by both portable and benchtop Raman spectrometers, the distribution of GSH in different tissues at centimeter scale can be displayed through Raman spectroscopy and Raman imaging, and the entire analysis process can be accomplished within 12 min. Accordingly, in vivo brain tissues of orthotopic GBM xenograft mice and ex vivo tissues of GBM patients are accurately differentiated with the microneedle, and the results are well consistent with tissue staining and postoperative pathological reports. In addition, the outline of tumor, peritumoral, and normal tissues can be indicated by the DTNB@Au@Ag microneedle for at least 56 days. Considering that the tumor tissues are quickly discriminated at the molecular level without the restriction of depth, the DTNB@Au@Ag microneedle is promising to be a powerful intraoperative diagnostic tool for surgery navigation.

Dual roles of HK3 in regulating the network between tumor cells and tumor-associated macrophages in neuroblastoma.

Neuroblastoma (NB) is the most common and deadliest extracranial solid tumor in children. Targeting tumor-associated macrophages (TAMs) is a strategy for attenuating tumor-promoting states. The crosstalk between cancer cells and TAMs plays a pivotal role in mediating tumor progression in NB. The overexpression of Hexokinase-3 (HK3), a pivotal enzyme in glucose metabolism, has been associated with poor prognosis in NB patients. Furthermore, it correlates with the infiltration of M2-like macrophages within NB tumors, indicating its significant involvement in tumor progression. Therefore, HK3 not only directly regulates the malignant biological behaviors of tumor cells, such as proliferation, migration, and invasion, but also recruits and polarizes M2-like macrophages through the PI3K/AKT-CXCL14 axis in neuroblastoma. The secretion of lactate and histone lactylation alterations within tumor cells accompanies this interaction. Additionally, elevated expression of HK3 in M2-TAMs was found at the same time. Modulating HK3 within M2-TAMs alters the biological behavior of tumor cells, as demonstrated by our in vitro studies. This study highlights the pivotal role of HK3 in the progression of NB malignancy and its intricate regulatory network with M2-TAMs. It establishes HK3 as a promising dual-functional biomarker and therapeutic target in combating neuroblastoma.

Homotypic Membrane-Enhanced Blood-Brain Barrier Crossing and Glioblastoma Targeting for Precise Surgical Resection and Photothermal Therapy.

The crossing of blood-brain barrier (BBB) is essential for glioblastoma (GBM) therapy, and homotypic targeting is an effective strategy to achieve BBB crossing. In this work, GBM patient-derived tumor cell membrane (GBM-PDTCM) is prepared to cloak gold nanorods (AuNRs). Relying on the high homology of the GBM-PDTCM to the brain cell membrane, GBM-PDTCM@AuNRs realize efficient BBB crossing and selective GBM targeting. Meanwhile, owing to the functionalization of Raman reporter and lipophilic fluorophore, GBM-PDTCM@AuNRs are able to generate fluorescence and Raman signals at GBM lesion, and almost all tumor can be precisely resected in 15 min by the guidance of dual signals, ameliorating the surgical treatment for advanced GBM. In addition, photothermal therapy for orthotopic xenograft mice is accomplished by intravenous injection of GBM-PDTCM@AuNRs, doubling the median survival time of the mice, which improves the nonsurgical treatment for early GBM. Therefore, benefiting from homotypic membrane-enhanced BBB crossing and GBM targeting, all-stage GBM can be treated with GBM-PDTCM@AuNRs in distinct ways, providing an alternative idea for the therapy of tumor in the brain.

Polarity Conversion of the Ag2S/AgInS2 Heterojunction by Radical-Induced Positive Feedback Polydopamine Adhesion for Signal-Switchable Photoelectrochemical Biosensing.

Efficient tuning of the polarity of photoactive nanomaterials is of great importance in improving the performance of photoelectrochemical (PEC) sensing platforms. Herein, polarity of the Ag2S/AgInS2 heterojunction is converted by radical-induced positive feedback polydopamine (PDA) adhesion, which is further employed to develop a signal-switchable PEC biosensor. In the nanocomposites, Ag2S and AgInS2 achieve electron-hole separation, exhibiting a strong anodic PEC response. Under the irradiation of light, the Ag2S/AgInS2 heterojunction is able to produce superoxide radical and hydroxyl radical intermediate species, leading to the polymerization of dopamine (DA) and the subsequent adhesion of PDA onto the Ag2S/AgInS2 heterojunction (Ag2S/AgInS2@PDA). By constructing a new electron-transfer pathway with PDA, the polarity of the Ag2S/AgInS2 heterojunction is converted, and the PEC response changes from anodic to cathodic photocurrents. In addition, since the photoreduction activity of PDA is stronger than that of the Ag2S/AgInS2 heterojunction, more superoxide radical can be produced by Ag2S/AgInS2@PDA once PDA is generated, thereby promoting the generation of PDA. Consequently, a positive feedback mechanism is established to enhance the polarity conversion of the Ag2S/AgInS2 heterojunction and amplify the responding to DA. As a result, the bioanalytical method is capable of sensitively quantifying DA in 10 orders of magnitude with an ultralow limit of detection. Moreover, the applicability of this biosensor in real samples is identified by measuring DA in fetal bovine serum and compared with a commercial ELISA method. Overall, this work offers an alternative perspective for adjusting photogenerated carriers of nanomaterials and designing high-performance PEC biosensors.

Chemical Mechanism-Dominated and Reporter-Tunable Surface-Enhanced Raman Scattering via Directional Supramolecular Assembly.

Molecular resonance can be strengthened by charge transfer, profiting chemical mechanism (CM)-related surface-enhanced Raman scattering (SERS). Herein a supramolecular assembly enabled SERS system is established by functionalizing para-sulfonatocalix[4]arene (pSC4) onto Au3Cu nanocrystals (NCs). Due to the cooperation of Au and Cu, pSC4 is directionally assembled on the surface of Au3Cu NCs via van der Waals force, enabling photoinduced and hydrogen bond-induced charge transfer, which remarkably enhances the Raman scattering of methylene blue (MB) captured by pSC4. In particular, for the C-N and C-C stretching of MB, the contributions of resonance Raman scattering increase up to 80%. In addition, the SERS system is able to display affinities of different host-guest interactions, and further employed to evaluate effects of drugs for Alzheimer's disease. In this work, charge transfer is realized by performing supramolecular assembly on the surface of plasmonic nanomaterials, providing an avenue to design CM-related and reporter-tunable SERS systems.

Enhancing Photoelectric Response of an Au@Ag/AgI Schottky Contact through Regulation of Localized Surface Plasmon Resonance.

Carrier generation and migration are both pivotal to photoelectric (PE) response. Formation of a Schottky contact is conducive to promote carrier migration but cannot fundamentally magnify carrier generation, limiting the eventual PE performance. In this work, an Au@Ag/AgI Schottky contact is established by in situ growth of AgI nanotriangles on the surface of Au@Ag nanoparticles (NPs), and PE enhancement of the Schottky contact is realized by regulating localized surface plasmon resonance (LSPR) properties. In comparison with Ag/AgI Schottky contact, assembly of Au NPs in the center of Ag NPs adjusts the dominated LSPR property from hot-electron transfer (HET) to plasmon-induced resonance energy transfer (PIRET). With the concurrent manipulation of HET and PIRET, additional energy can be employed for carrier generation, while photogenerated electrons offset by hot electrons are reduced, which jointly enlarges PE responses of the Au@Ag/AgI Schottky contact up to 4 times. Benefitted from the etching of thiols to Ag-based materials, the Au@Ag/AgI Schottky contact is further applied to the construction of a photoelectrochemical cysteine sensor. This work proposes a general strategy to enhance PE responses of Schottky contacts, which may advance the design of LSPR-related PE systems.

Modulating Polarization of Perovskite-Based Heterostructures via In Situ Semiconductor Generation and Enzyme Catalysis for Signal-Switchable Photoelectrochemical Biosensing.

Polarization of photoactive materials in current photoelectric (PE) systems is difficult to be adjusted, and thus electron-transfer routes of these systems are unchangeable, which limits their performance in photoelectrochemical (PEC) analysis. Herein, we attempted to modulate the polarization of perovskite-based heterostructures by both in situ semiconductor generation and enzyme catalysis. Owing to their band alignments, Cs3Bi2Br9 quantum dots (QDs) and BiOBr are confirmed to construct a Z-scheme structure, leading to a large anodic photocurrent. In the presence of ascorbic acid 2-phosphate (AAP), BiPO4 is generated on the surface of the Cs3Bi2Br9 QDs/BiOBr heterostructure, reassigning energy bands of BiOBr. Accordingly, polarization of the photoactive materials is converted, and a new Z-scheme structure with a reversed electron-transfer route is constructed, which leads to an evident cathodic photocurrent. Furthermore, abundant electron donors can be obtained by catalyzing AAP with alkaline phosphatase (ALP). In this case, photogenerated holes in BiOBr are preferentially annihilated by electron donors, thereby blocking transfer of photogenerated electrons in the Cs3Bi2Br9 QDs/BiOBr/BiPO4 heterostructure. Consequently, a second polarization conversion is triggered by enzyme catalysis, resulting in the recovery of an anodic photocurrent. Benefited from the polarization conversion, a PEC biosensor with a feature of two-wing signal switch is designed, which remarkably enlarges the range of the signal response and subsequently improves the analytical performance. As a result, ALP in small volume of human serum can be quantified with this method. In this work, polarization of perovskite-based photoactive materials is tuned, proposing an alternative perspective on the design of advanced PE systems.

A Simple and Efficient Method to Generate Dual Site-Specific Conjugation ADCs with Cysteine Residue and an Unnatural Amino Acid.

Antibody-drug conjugates (ADCs) are complex pharmaceutical molecules that combine monoclonal antibodies with biologically active drugs through chemical linkers. ADCs are designed to specifically kill disease cells by utilizing the target specificity of antibodies and the cytotoxicity of chemical drugs. However, the traditional ADCs were only applied to a few disease targets because of some limitations such as the huge molecular weight, the uncontrollable coupling reactions, and a single mechanism of action. Here we report a simple, one-pot, successive reaction method to produce dual payload conjugates with the site-specifically engineered cysteine and p-acetyl-phenylalanine using Herceptin (trastuzumab), an anti-HER2 antibody drug widely used for breast cancer treatment, as a tool molecule. This strategy enables antibodies to conjugate with two mechanistically distinct cytotoxic drugs through different functional groups sequentially, therefore, rendering the newly designed ADCs with functional diversity and the potential to overcome drug resistance and enhance the therapeutic efficacy.

Applications of DNA-nanozyme-based sensors.

Since the discovery of the enzyme-like activities of nanomaterials, the study of nanozymes has become one of the most popular research frontiers of diverse areas including biosensors. DNA also plays a very important role in the construction of biosensors. Thus, the idea of combined applications of nanozymes with DNA (DNA-nanozyme) is very attractive for the development of nanozyme-based biosensors, which has attracted considerable interest of researchers. To date, many sensors based on DNA-functionalized or templated nanozymes have been reported for the detection of various targets and highly accelerated the development of nanozyme-based sensors. In this review, we summarize the main applications and advances of DNA-nanozyme-based sensors. Additionally, perspectives and challenges are also discussed at the end of the review.

Construction of Molecular Sensing and Logic Systems Based on Site-Occupying Effect-Modulated MOF-DNA Interaction.

Interactions between metal-organic frameworks (MOFs) and nucleic acids are of great importance in molecular assembly. However, current MOF-nucleic acid interactions lack diversity and are normally realized in an uncontrollable manner. Herein, the interaction of zirconium-based MOFs (Zr-MOFs) with nucleic acids is enabled by the formation of Zr-O-P bonds and further manipulated by a phosphate-induced site-occupying effect. Covering Zr ions in clusters of MOFs with phosphates impedes the formation of Zr-O-P bonds with nucleic acids, rendering the MOF-nucleic acid interaction tunable and stimulus-responsive. Notably, the experimental results demonstrate that various phosphates, Zr-MOFs, and nucleic acids can all be adopted in the tunable interaction. On the basis of these findings, fluorescent DNA and typical Zr-MOFs are proposed as functional probe-quencher pairs to establish molecular sensing and logic systems. Accordingly, alkaline phosphatase and inorganic pyrophosphatase can be quantified simultaneously, and the overall relation of different phosphates and phosphatases is facilely displayed. The work provides a general strategy for modulating MOF-nucleic acid interactions, which is conducive to the development of molecular intelligent systems.

Sensitive determination of formamidopyrimidine DNA glucosylase based on phosphate group-modulated multi-enzyme catalysis and fluorescent copper nanoclusters.

In this work, a method for quantifying the activity of formamidopyrimidine DNA glucosylase (Fpg) was designed based on phosphate group (P)-modulated multi-enzyme catalysis and fluorescent copper nanoclusters (CuNCs). By eliminating 8-oxoguanine from double-stranded DNA, Fpg generates a nick with P at both 3' and 5' termini. Subsequently, part of the DNA is digested by 5'P-activated lambda exonuclease (λ Exo), and the generated 3'P disables exonuclease I (Exo I), resulting in the generation of single-stranded DNA containing poly(thymine) (poly(T)). Using poly(T) as templates, CuNCs were prepared to emit intense fluorescence as the readout of this method. However, in the absence of Fpg, the originally modified 5'P triggers the digestion of λ Exo. In this case, fluorescence emission is not obtained because CuNCs cannot be formed without DNA templates. Therefore, the catalysis of λ Exo and Exo I can be tuned by 5'P and 3'P, which can be further used to determine the activity of Fpg. The fluorescent Fpg biosensor works in a "signal-on" manner with the feature of "zero" background noise, and thus shows desirable analytical features and good performance. Besides, Fpg in serum samples and cell lysate could be accurately detected with the biosensor, indicating the great value of the proposed system in practical and clinical analysis.

Spectrum-Quantified Morphological Evolution of Enzyme-Protected Silver Nanotriangles by DNA-Guided Postshaping.

Quantitative morphological evolution is of great importance in nanochemistry. In this work, morphology of silver nanotriangles (AgNTs) is quantitatively evolved under the guidance of DNA. First, intact AgNTs are prepared relying on the protection of horseradish peroxidase. Then different regions of AgNTs are sequentially etched by C-rich DNA, leading to DNA-guided postshaping of AgNTs. In combination with atomically resolved images and theoretical simulation, a model is established to track the postshaping process. Since real-time morphological evolution of AgNTs is determined with spectra, a series of AgNTs with specific corners can be obtained by controlling incubation time. The DNA-guided postshaping is sequence and structure dual-dependent, and a mechanism is proposed based on metal-base interaction, surface energy of faces, and freedom of DNA structure. In addition, the postshaping is further used to design DNA-mediated biosensors. This study provides a precise and quantitative method of controlling morphology of anisotropic metallic nanomaterials.

Photoelectrochemical Approach to Apoptosis Evaluation via Multi-Functional Peptide- and Electrostatic Attraction-Guided Excitonic Response.

The excitonic response between nanomaterials is distance-dependent, and thus, interparticle distance is a key factor in fabricating diverse photoelectrochemical (PEC) systems. Current studies focus on DNA-mediated regulation of interparticle distance. However, limited by high demands of base-pairing and flexibility of DNA, it is hard for DNA to achieve precise regulation, especially in a short distance. To pursue better PEC performances in bioanalyses, alternative biological materials should be explored to replace DNA as new "distance controllers". In this work, a peptide with three functional sequences is designed to control interparticle distance between positive-charged Au nanoparticles ((+) AuNPs) and negative-charged CdTe quantum dots ((-) CdTe QDs). Relying on the function of binding sequence, (+) AuNPs and (-) CdTe QDs may be separated to a certain distance by the multifunctional peptide. In this case, the excitonic response is relatively weak, and an evident PEC response can be observed. Because it contains the substrate sequence of caspase-3, the peptide is cleaved in the presence of caspase-3. As a result, without the support of intact peptide, electrostatic attraction plays a dominant role, leading to the aggregation of oppositely charged AuNPs and CdTe QDs, which strengthens the excitonic response and attenuates the PEC response. On the basis of these principles, a novel PEC approach was fabricated to sensitively quantify caspase-3. Meanwhile, caspase-3 in staurosporine-treated A549 cells are also determined by the approach, and the obtained results agree well with the fluorescent intensity of confocal images, manifesting that the proposed PEC method can monitor apoptosis in a label-free strategy. Overall, the study reveals the capability of peptides in controlling interparticle distance of nanomaterials, which may accelerate the development of peptide-based PEC analytical methods.

Amino Acid-Capped Water-Soluble Near-Infrared Region CuInS2/ZnS Quantum Dots for Selective Cadmium Ion Determination and Multicolor Cell Imaging.

Although attractive for their low toxicity, CuInS2/ZnS core/shell quantum dots (CIS/ZnS QDs) still suffer from poor luminescence efficiency and poor water solubility. Herein, two amino acids (AAs), i.e., cysteine (Cys) and threonine (Thr), are used to tune the properties of CIS/ZnS QDs by capping them in both core and shell. It is found that Thr can regulate the density of Cys on the surface of QDs, thus causing a synergistic effect on the enhancement of photoluminescence (PL) intensity. Capping in the shell mainly leads to the enhancement of PL intensity, and capping in the core results in a red-shift of PL wavelength. Accordingly, a new kind of near-infrared region CIS/ZnS QDs with improved optical properties has been prepared. In addition, the Cys- and Thr-capped CIS/ZnS QDs possess outstanding water solubility and biocompatibility. In this work, the QDs are further employed in Cd2+ determination and multicolor imaging, indicating their potential applications. Relying on the enhancement of PL intensity via cation exchange, the Cys- and Thr-capped CIS/ZnS QDs can sense Cd2+ sensitively. Notably, because ZnS shells of the QDs will not be affected by Zn2+, the analytical method can discriminate Cd2+ from Zn2+ depending on the inherent characteristics of QDs. Moreover, intercellular Cd2+ can also be evaluated by the bright PL from the QDs, and the QDs can achieve multicolor imaging. Overall, this work demonstrates that various properties of QDs may be tuned by capping with AAs, and AA-capped QDs are of great value in advanced biosensing and bioimaging.

Graphene Oxide-Assisted and DNA-Modulated SERS of AuCu Alloy for the Fabrication of Apurinic/Apyrimidinic Endonuclease 1 Biosensor.

Fabrication of high-performance surface-enhanced Raman scattering (SERS) biosensors relies on the coordination of SERS substrates and sensing strategies. Herein, a SERS active AuCu alloy with a starfish-like structure is prepared using a surfactant-free method. By covering the anisotropic AuCu alloy with graphene oxide (GO), enhanced SERS activity is obtained owing to graphene-enhanced Raman scattering and assembly of Raman reporters. Besides, stability of SERS is promoted based on the protection of GO to the AuCu alloy. Meanwhile, it is found that SERS activity of AuCu/GO can be regulated by DNA. The regulation is sequence and length dual-dependent, and short polyT reveals the strongest ability of enhancing the SERS activity. Relying on this phenomenon, a SERS biosensor is designed to quantify apurinic/apyrimidinic endonuclease 1 (APE1). Because of the APE1-induced cycling amplification, the biosensor is able to detect APE1 sensitively and selectively. In addition, APE1 in human serum is analyzed by the SERS biosensor and enzyme-linked immunosorbent assay (ELISA). The data from the SERS method are superior to that from ELISA, indicating great potential of this biosensor in clinical applications.

A novel electrochemiluminescence biosensor based on S-doped yttrium oxide ultrathin nanosheets for the detection of anti-Dig antibodies.

New S-doped yttrium oxide ultrathin nanosheets (NSs) were synthesized which had good electrochemiluminescence (ECL) properties. Through combining these NSs with small molecule linked DNA as the substrate, a novel ECL biosensor was constructed for the detection of protein biomarkers with an acceptable performance.

Fluorescence Regulation of Poly(thymine)-Templated Copper Nanoparticles via an Enzyme-Triggered Reaction toward Sensitive and Selective Detection of Alkaline Phosphatase.

The activity of alkaline phosphatase (ALP) is a crucial index of blood routine examinations, since the concentration of ALP is highly associated with various human diseases. To address the demands of clinical tests, efforts should be made to develop more approaches that can sense ALP in real samples. Recently, we find that fluorescence of poly(30T)-templated copper nanoparticles (CuNPs) can be directly and effectively quenched by pyrophosphate ion (PPi), providing new perspective in designing sensitive biosensors based on DNA-templated CuNPs. In addition, it has been confirmed that phosphate ion (Pi), product of PPi hydrolysis, does not affect the intense fluorescence of CuNPs. Since ALP can specifically hydrolyze PPi into Pi, fluorescence of CuNPs is thus regulated by an ALP-triggered reaction, and a novel ALP biosensor is successfully developed. As a result, ALP is sensitively and selectively quantified with a wide linear range of 6.0 × 10-2 U/L to 6.0 × 102 U/L and a low detection limit of 3.5 × 10-2 U/L. Besides, two typical inhibitors of ALP are evaluated by this analytical method, and different inhibitory effects are indicated. More importantly, by challenging this biosensor with real human serums, the obtained results get a fine match with the data from clinical tests, and the serum sample from a patient with liver disease is clearly distinguished, suggesting promising applications of this biosensor in clinical diagnosis.

Sequence and Structure Dual-Dependent Interaction between Small Molecules and DNA for the Detection of Residual Silver Ions in As-Prepared Silver Nanomaterials.

Investigations on interaction between small molecules and DNA are the basis of designing advanced bioanalytical systems. We herein propose a novel interaction between heterocyclic aromatic compounds (HACs) and single-stranded DNA (ssDNA). Taking methylene blue (MB) as a typical HAC, it is found that MB can interact with cytosine (C)-rich ssDNA in an enthalpy-driven process. The interaction between MB and C-rich ssDNA is sequence and structure dual-dependent: at least three consecutive C and single-stranded structure are necessary, affecting the fluorescence response of metal nanoparticles. With the exception of the single-stranded structure, double-stranded, i-motif, and C-Ag-C mismatch structures will remarkably impede the interaction with MB. UV-vis absorption, fluorescent, and electrochemical curves demonstrate that the conjugated system, electron transition, and electron transfer of MB are remarkably affected by MB-C-rich ssDNA interaction. In particular, the absorption peak of MB at 664 nm decreases, and a new peak at 538 nm emerges. Therefore, the interaction can be characterized by a colorimetric and ratiometric signal. Relying on the inhibition of C-Ag-C mismatch and the enhanced analytical performances of the ratiometic signal, the MB-C-rich ssDNA interaction is further employed to quantify silver ions (Ag+) selectively and sensitively. In addition, since silver nanomaterials cannot introduce C-Ag-C mismatch, the fabricated biosensor is able to sense residual Ag+ in silver nanoparticles and silver nanowires, which is of great value in the precise and economical preparation of silver nanomaterials.

A label-free fluorescent adenosine triphosphate biosensor via overhanging aptamer-triggered enzyme protection and target recycling amplification.

Herein, a label-free fluorescent adenosine triphosphate (ATP) aptasensor is fabricated with a DNA hairpin and an overhanging aptamer. In the presence of ATP, the overhanging sequences of the aptamer may form preferred substrates of exo III, and thus trigger the enzyme-assisted amplification, which results in the release of G-rich sequences. Free G-rich sequences subsequently generate an enhanced flourescent signal by binding with thioflavin T. However, if ATP is absent, the overhanging sequence can induce steric hindrance and protect the DNA hairpin against the digestion of exo III, significantly reducing the noise of this biosensor. Accordingly, the signal-to-noise ratio of the sensing system is greatly improved, which ensures the desirable analytical performance of the proposed aptasensor both in pure samples and real samples.

Aggregation of Individual Sensing Units for Signal Accumulation: Conversion of Liquid-Phase Colorimetric Assay into Enhanced Surface-Tethered Electrochemical Analysis.

A novel concept is proposed for converting liquid-phase colorimetric assay into enhanced surface-tethered electrochemical analysis, which is based on the analyte-induced formation of a network architecture of metal nanoparticles (MNs). In a proof-of-concept trial, thymine-functionalized silver nanoparticle (Ag-T) is designed as the sensing unit for Hg(2+) determination. Through a specific T-Hg(2+)-T coordination, the validation system based on functionalized sensing units not only can perform well in a colorimetric Hg(2+) assay, but also can be developed into a more sensitive and stable electrochemical Hg(2+) sensor. In electrochemical analysis, the simple principle of analyte-induced aggregation of MNs can be used as a dual signal amplification strategy for significantly improving the detection sensitivity. More importantly, those numerous and diverse colorimetric assays that rely on the target-induced aggregation of MNs can be augmented to satisfy the ambitious demands of sensitive analysis by converting them into electrochemical assays via this approach.