Reticular construction of a two-dimensional Ag₁₂ cluster-assembled material for rapid and selective luminescent sensing of antibiotics in aqueous media

Abstract

Silver cluster-assembled materials (SCAMs) represent a promising class of luminescent solids, uniting atomically precise metal core architectures with crystalline framework design for tunable optical performance. Despite offering enhanced structural integrity over discrete silver nanoclusters, their broader application—particularly in aqueous-phase sensing—remains constrained by limited chemical and structural stability. Herein, we report TUS 8, a two-dimensional SCAM constructed from dodecanuclear Ag₁₂ nodes and 1,1′-sulfonyldiimidazole (SDI) linkers. Single-crystal X-ray diffraction reveals a (2,4)-connected network in the P2₁/c space group featuring slightly distorted, hollow cuboctahedral Ag₁₂ cores capped by μ₄-tert-butylthiolates and μ₂-trifluoroacetates. These layers stack via noncovalent interactions, forming a chemically robust porous architecture. TUS 8 exhibits intense ultraviolet absorption (λ_ex = 215 nm) and strong aqueous photoluminescence emission at 344 nm, with a mono-exponential lifetime of 4.62 ns and an absolute quantum yield of 26.3%, among the highest reported for silver-based MOFs in water. The rigid framework and Ag⋯Ag interactions suppress non-radiative decay to enhance luminescence performance in aqueous media, while the material's retention of high crystallinity after immersion in various solvents underscores its chemical robustness. Leveraging these features, TUS 8 functions as a recyclable luminescent sensor for antibiotic detection in water. Distinct PL responses are observed for nitrofurans, nitroimidazoles, and chloramphenicol, with quenching constants up to 2.4 × 10³ M⁻¹ and detection limits as low as 311 μM. This study highlights the potential of cluster-based reticular design for creating durable, water-stable, and highly emissive sensing platforms.

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Introduction

Metal nanoclusters (NCs), situated at the interface between discrete atoms and larger nanoparticles, have emerged as a unique class of functional materials with atomically precise structures and size-dependent properties.^1–12 Their ultrasmall core dimensions (typically <3 nm) and quantized electronic states endow them with exceptional properties such as strong photoluminescence, high surface-to-volume ratio, and rich redox chemistry.^13–17 These attributes have enabled a broad spectrum of applications spanning catalysis,¹⁸ sensing,¹⁹ bioimaging,²⁰ and energy conversion.¹¹ In particular, the ability to tailor both the metal core and the ligand shell with atomic precision renders NCs highly attractive platforms for materials innovation at the molecular level. Among the various metal NCs, silver-based nanoclusters (Ag NCs) have garnered sustained attention due to their versatile coordination chemistry, distinctive structural motifs, and intense photoluminescence driven by metal-centered electronic transitions.^21–25 Nevertheless, their broader application has been substantially constrained by their inherent chemical lability. Unlike more inert noble metal counterparts, Ag NCs are highly prone to oxidative degradation when exposed to air, light, or aqueous environments. This vulnerability originates from the relatively weak metal–ligand bonding and the high surface reactivity of silver atoms in ultrasmall clusters, which facilitates structural decomposition and loss of functionality under ambient conditions. As a result, achieving long-term stability remains a major challenge in the practical deployment of Ag NCs across sensing, catalytic, and biomedical domains.

To address these challenges, recent efforts have shifted toward the assembly of Ag NCs into extended architectures, wherein enhanced stability is achieved via inter-cluster interactions or coordination with stabilizing moieties.^26–28 While non-covalent self-assembly of discrete Ag NCs can offer modest improvements in structural robustness, such strategies often lack the architectural precision and chemical tunability required for fine control over material properties.^29,30 In contrast, reticular chemistry³¹—a design strategy rooted in the deliberate linkage of well-defined building units into crystalline frameworks—has opened up compelling possibilities for organizing Ag NCs into ordered networks. In this context, silver cluster-assembled materials (SCAMs), formed by bridging Ag(I) cluster nodes with organic linkers, have emerged as a promising structural platform that combines the inherent properties of Ag NCs with the design versatility of metal–organic frameworks (MOFs).^32,33 The integration of multidentate organic linkers into the architecture of SCAMs has proven to be a powerful strategy for achieving both structural precision and functional tunability. Directional coordination between the organic linkers and Ag cluster nodes enables the formation of well-defined crystalline frameworks with controllable dimensionality and topological diversity. Moreover, the inherent modularity of these linkers provides a versatile handle for tailoring key material features—including pore architecture, surface chemistry, and electronic environment—which in turn facilitates selective host–guest interactions for targeted applications. The resulting framework rigidity and connectivity not only reinforce the structural integrity of the assemblies but also enhance their long-term photophysical stability, addressing a central challenge in the development of Ag-based materials for practical deployment.

Pioneering work by Zang and co-workers demonstrated the viability of reticular strategies for stabilizing Ag nanoclusters by replacing labile surface ligands on Ag₁₂ clusters with rigid bipyridyl linkers.³⁴ This led to the formation of two-dimensional (2D) SCAMs exhibiting significantly enhanced structural robustness and improved photoluminescence quantum yields. Beyond the extensively studied pyridyl-based systems, a wide variety of organic linkers—including pyrazine,³⁵ azopyridine,³⁶ porphyrin,³⁷ spirobifluorene,³⁸ imidazolyl,³⁹ carboxylate,⁴⁰ thiourea,⁴¹ and others—have been employed to construct SCAMs with diverse dimensionalities (1D, 2D, and 3D) and functional attributes. In parallel, progress has also been made in expanding the structural library of silver cluster nodes. While Ag₁₂ clusters remain the prototypical building blocks,^42–45 numerous SCAMs have been assembled from alternative Ag NCs comprising different nuclearities, including Ag₅,⁴⁶ Ag₉,⁴⁷ Ag₁₀,⁴⁸ Ag₁₁,⁴⁹ Ag₁₄,³⁶ Ag₂₀,⁵⁰ and Ag₂₇ ⁵¹ clusters. These efforts underscore the structural tunability and modularity of the SCAM platform, driven by both cluster nuclearity and linker geometry. However, despite the increasing structural diversity and elegance of these systems, the translation of SCAMs into solution-phase functional materials—particularly for luminescence-based sensing—remains relatively underexplored, largely due to lingering concerns about framework stability under aqueous or photochemical conditions.

Motivated by these considerations, we have developed a new 2D SCAM based on Ag₁₂ cluster nodes and a conjugated, electron-rich, S,O-containing linker molecule, 1,1′-sulfonyldiimidazole (SDI). This bifunctional linker combines the rigidity and π-conjugation of imidazole units with the electron-withdrawing sulfonyl group, which not only facilitates robust coordination with silver ions but also imparts hydrophilicity and enhanced chemical stability to the framework. The resulting SDI–Ag₁₂ SCAM, designated as TUS 8, exhibits exceptional structural integrity in aqueous environments, overcoming one of the most persistent limitations of Ag NC-derived materials. Beyond structural stability, TUS 8 also demonstrates rapid, reversible, and highly selective photoluminescent sensing of antibiotics in water. The framework's emission behavior is exquisitely sensitive to the nature of the analyte, enabling discrimination between multiple drug molecules based on the direction and magnitude of the emission shift. Specifically, nitrofuran-based antibiotics such as furazolidone and nitrofurazone, which are strongly electron-withdrawing and reduce local polarizability, induce a hypsochromic (blue) shift, while nitroimidazole drugs like ornidazole and dimetridazole—with their conjugated imidazole units—engage in imidazole–imidazole interactions with the SDI linkers, enhancing conjugation and yielding a bathochromic (red) shift. Chloramphenicol, a structurally distinct antibiotic, produces a subtle red shift, consistent with weaker guest–host interactions. Importantly, the SCAM retains its sensing performance over multiple cycles, underscoring its outstanding recyclability and operational stability. This combination of aqueous robustness, selective responsiveness, and reusability highlights the TUS 8 SCAM as a highly promising candidate for real-time antibiotic monitoring and broader environmental or biomedical sensing applications. More broadly, this study illustrates how rational linker design in cluster-based reticular frameworks can synergistically enhance both structural resilience and functional performance, offering new directions in the development of next-generation luminescent materials.

Results and discussion

The reticular construction of TUS 8 was accomplished via a two-step assembly strategy that capitalized on the preformation of atomically precise Ag₁₂ NC nodes, followed by their directional linkage with an S,O-rich organic ligand. Initially, the reaction between [AgS^tBu]_n and CF₃COOAg in a 1 : 1 (v/v) chloroform/ethanol binary solvent system facilitated the in situ generation of discrete Ag₁₂ clusters. The turbidity observed upon dissolution of [AgS^tBu]_n, which gradually transitioned to a clear solution upon addition of CF₃COOAg, indicated a dynamic ligand exchange process involving thiolate and trifluoroacetate anions. This transformation likely induced the rearrangement of Ag⁺ ions into a dodecanuclear architecture stabilized by a mixed-ligand shell, wherein weakly bound ancillary ligands rendered the clusters amenable to subsequent framework assembly. In parallel, the SDI linker molecule, dissolved in the same solvent medium, was introduced dropwise to the Ag₁₂ cluster solution under ambient conditions. The polar sulfonyl moiety of SDI, combined with its rigid and conjugated imidazole donors, promoted directional coordination with the silver centers, driving the self-assembly into an extended 2D framework through dynamic coordination equilibrium. After standing undisturbed in the dark at room temperature for 72 hours, the reaction yielded colorless rhombic single crystals of TUS 8 in 78% isolated yield based on silver. Optical microscopy analysis revealed well-defined, three-dimensionally grown crystals with sharply faceted rhombus-like morphology, consistent with high crystallinity and uniform framework propagation along specific lattice directions (Fig. 1 and S1). This controlled growth reflects the balance between kinetically labile Ag–ligand interactions and thermodynamically favorable cluster–linker coordination.

Fig. 1 Depiction of the synthetic pathway leading to TUS 8 single crystals. Optical microscopy image of a representative crystal collected from the bottom of the reaction vial is included. Color code: N, blue; S, yellow; O, red; C, grey; H, white.

Single-crystal X-ray diffraction (SCXRD) analysis provided unambiguous structural resolution of the TUS 8 framework, revealing a highly ordered 2D cluster-assembled material crystallizing in the monoclinic space group P2₁/c (No. 14) (Table S1). The fundamental building unit is a dodecanuclear Ag₁₂ NC that adopts a slightly distorted hollow cuboctahedral-like geometry, composed of twelve Ag(I) ions arranged in an edge-sharing polyhedron characterized by eight triangular and six skew quadrilateral faces—bearing resemblance to an Archimedean solid (Fig. 2a). Within the cluster, the twelve Ag atoms are distributed over three distinct structural layers: a central hexagonal ring of six silver atoms defining the equatorial plane, flanked by two parallel triangular layers, each comprising three silver centers arranged in a capping configuration that is inclined relative to the equator (Fig. S2). This multilayered configuration gives rise to a compact, albeit distorted, cuboctahedral-like structure, stabilized by prominent argentophilic interactions, as reflected in the average Ag–Ag distance of 3.095 Å (Table S2)—notably shorter than the van der Waals contact distance between silver atoms (3.44 Å). Surface passivation of the Ag₁₂ core is achieved through the coordination of six tert-butylthiolate (S^tBu) ligands and six trifluoroacetate (CF₃COO⁻) anions. Each S^tBu ligand adopts a tetradentate μ₄-η¹:η¹:η¹:η¹ binding mode, bridging four silver atoms spanning both the equatorial and axial planes (Fig. 2b), with an average Ag–S bond length of 2.510 Å (Table S3). This extensive bridging imparts rigidity to the cluster core while sterically shielding the Ag(I) centers from undesirable interactions with extraneous species. Complementing this protection, each CF₃COO⁻ anion bridges two Ag atoms—one from the triangular cap and one from the hexagonal midplane—via μ₂-η¹:η¹ coordination through its oxygen atoms (average Ag–O distance = 2.454 Å; Table S4), thereby forming a five-membered Ag–carboxylate coordination ring at the cluster periphery (Fig. 2c). Notably, the distribution of CF₃COO⁻ coordination across the midplane is asymmetric: two Ag atoms remain uncoordinated to any carboxylate, two are coordinated to a single CF₃COO⁻ anion each, and the remaining two are bound to two distinct CF₃COO⁻ anions each. Critically, the propagation of the framework is driven by the bidentate coordination of the SDI linker, which binds to four Ag atoms located in the central hexagonal layer through terminal imidazole nitrogen atoms (Fig. 2d and e) (average Ag–N distance = 2.228 Å; Table S5). The observation that only four SDI linkers coordinate to the Ag₁₂ cluster—specifically to four silver atoms located in the central hexagonal layer—contrasts with the coordination pattern commonly observed in related Ag₁₂-based SCAMs, where six organic linkers typically bind to six peripheral silver sites. This deviation can be attributed to the combined influence of steric hindrance, electronic saturation, and the geometric characteristics of the SDI linker. In the present structure, the uneven distribution of CF₃COO⁻ coordination across the midplane creates spatial and electronic congestion at certain midplane Ag sites, thereby limiting their accessibility for coordination with additional linkers such as SDI. Furthermore, the SDI linker features two terminal imidazole donors connected by a rigid sulfonyl spacer, which imposes geometric constraints on its binding mode. Coordination to four symmetrically disposed Ag atoms in the midplane likely represents the most favorable configuration, minimizing steric repulsion and avoiding strain. The remaining two Ag atoms in the hexagonal layer may be sterically hindered or electronically saturated due to the presence of adjacent CF₃COO⁻ and S^tBu ligands, thus disfavoring further coordination by SDI. Each SDI linker functions as a linear ditopic spacer, bridging adjacent Ag₁₂ nodes along the a and b crystallographic axes. This coordination geometry results in a well-defined (2,4)-connected 2D network, wherein each Ag₁₂ cluster serves as a 4-connected inorganic node, and each SDI molecule acts as a 2-connected organic linker. The layers extend periodically within the ab-plane, forming an ordered array of cluster-linker units with long-range crystallographic order (Fig. 3a). Notably, the 2D sheets are stacked along the c-axis through interlayer van der Waals and dipolar interactions involving the sulfonyl and alkyl moieties of the SDI and S^tBu ligands, respectively. This vertical stacking constructs a 3D layered architecture with accessible void spaces. The interlayer distance, measured at 7.078 Å from the crystallographic data (Fig. S8), defines a regular spacing between adjacent 2D layers and permits the formation of vertically aligned 1D nanochannels orthogonal to the cluster layers. To assess the permanent porosity of TUS 8, N₂ adsorption–desorption measurements were performed at 77 K. The isotherm exhibits a classical Type-I profile characterized by a sharp uptake at low relative pressures (P/P₀ < 0.01), indicative of microporous behavior (Fig. S9a). Analysis using the Brunauer–Emmett–Teller (BET) model yielded a specific surface area of 85.4 m² g⁻¹ (Fig. S9b). It is noteworthy that SCAMs, including TUS 8, often display moderate surface areas owing to the large size of the multinuclear cluster nodes combined with the presence of protective ligands, which inherently reduce accessible porosity. Despite this, the SDI linker plays a pivotal role in constructing a stable reticular framework and mediating selective luminescence sensing.

Fig. 2 Evolution of the Ag₁₂ NC node: (a) cuboctahedron representing the Ag₁₂ core, followed by the stepwise addition of (b) S^tBu ligands, (c) CF₃COO− ligands, and (d) organic linkers. (e) The resulting Ag₁₂ cluster functions as a 4-connected node linked to four SDI molecules. H atoms are omitted for visual clarity.

Fig. 3 (a) 2D planar network of TUS 8 featuring Ag₁₂ node–linker connectivity; (b) 3D representation of the overall architecture. To enhance clarity, occasionally ligands and H atoms are not displayed.

The phase purity and structural integrity of bulk TUS 8 samples were validated through powder X-ray diffraction (PXRD) analysis. The experimentally obtained PXRD pattern of the activated material closely matches the simulated diffractogram derived from SCXRD data, confirming the successful bulk crystallization of TUS 8 in a single, well-defined phase (Fig. 4a). No extraneous reflections or peak broadening were observed, indicating high crystallinity and phase uniformity across the sample. To gain insights into the chemical composition and oxidation states of the constituent elements, X-ray photoelectron spectroscopy (XPS) was conducted under ultrahigh vacuum conditions using Mg Kα radiation. The wide-scan survey spectrum (Fig. 4b) revealed the presence of Ag, S, N, O, F, and C elements—corresponding to the Ag₁₂ cluster core, S^tBu and CF₃COO⁻ ligands, and the SDI linkers. High-resolution scans further elucidated the electronic environment of each element. The Ag 3d region (Fig. S10a) exhibits two prominent peaks at binding energies of 367.1 eV and 373.1 eV, attributable to Ag 3d_5/2 and Ag 3d_3/2, respectively. The 6.0 eV spin–orbit splitting is characteristic of monovalent silver (Ag⁺), consistent with a d¹⁰ configuration and the closed-shell nature of Ag(I) centers in the NC. The S 2p region displays two distinct doublets. The first, centered at 160.1 eV (S 2p_3/2) and 162.1 eV (S 2p_1/2), corresponds to thiolate sulfur (S⁻) bound to silver, originating from the S^tBu ligands. The second doublet at higher binding energies—167.1 eV and 168.4 eV—is indicative of oxidized sulfur species associated with the sulfonyl (–SO₂⁻) group in the SDI linker (Fig. S10d). The O 1s spectrum (Fig. S10e) reveals a primary peak at 530.1 eV, assignable to the coordinated oxygen atoms in carboxylate groups (Ag–O–C), with potential contributions from the sulfonyl oxygen atoms. The N 1s high-resolution spectrum (Fig. S10f) displays two components at 397.9 eV and 399.5 eV. The lower-energy peak (397.9 eV) is assigned to the imidazole nitrogen atoms (N3) coordinating to Ag(I) centers. The higher-energy feature (399.5 eV) corresponds to the non-coordinating (N1) nitrogen atoms substituted by the sulfonyl bridge, which retain a lone pair but do not bind to metal centers. Meanwhile, the F 1s peak centered at 686.6 eV (Fig. S10c) corresponds to fluorine atoms from the CF₃COO⁻ ligands, further corroborating the presence of the ancillary carboxylates. Collectively, these XPS findings validate the chemical identity of all framework components and confirm the preservation of Ag–S, Ag–N, and Ag–O coordination environments in the bulk material. To evaluate chemical robustness, TUS 8 single crystals were subjected to solvent immersion tests in various polar and nonpolar media (e.g., H₂O, methanol, acetone, DCM, hexane) for 24 hours. PXRD patterns recorded after solvent exposure (Fig. 4c) remained essentially unchanged, suggesting strong framework integrity and minimal ligand displacement. This chemical resilience, combined with the high crystallinity, underscores the potential of TUS 8 for deployment in aqueous or solvent environments. Thermal stability was assessed via thermogravimetric analysis (TGA), which revealed a minor weight loss below 110 °C attributed to surface-adsorbed solvents, followed by structural decomposition at higher temperatures (Fig. S11), indicating moderate thermal robustness under dry conditions. Morphological characterization through scanning electron microscopy (SEM) revealed well-faceted, rhombic single crystals with smooth surfaces (Fig. 4d). Energy-dispersive X-ray spectroscopy (EDX) elemental mapping corroborated the homogeneous distribution of Ag, S, N, F, and O elements across the crystal surface, in agreement with the compositional insights obtained from XPS. The combined SEM–EDX and XPS analyses confirm the uniformity, stoichiometry, and stability of TUS 8, supporting its structural fidelity and potential for practical applications.

Fig. 4 (a) Overlay of simulated and measured XRD patterns confirming the crystallinity of TUS 8; (b) Wide-scan XPS spectrum indicating surface elemental composition; (c) PXRD analysis of TUS 8 after 24 h exposure to various solvents; and (d) SEM micrograph of TUS 8 and corresponding EDX elemental maps displaying the spatial distribution of each element in separate panels.

Optical absorption and photoluminescence studies were conducted to probe the electronic structure and emissive behavior of TUS 8, particularly in aqueous dispersion, given the material's notable water stability. The UV–Vis spectrum of TUS 8 in water reveals a prominent absorption band centered at 215 nm (Fig. 5a), which corresponds to π → π* transitions primarily localized on the imidazole units of the SDI linker. For comparison, the free SDI linker exhibits a slightly red-shifted absorption maximum at 218 nm (Fig. S12), suggesting that incorporation into the extended coordination network induces subtle perturbations in the electronic environment of the linker. Although the shift is minor, it is not insignificant—it reflects a change in orbital overlap and electronic polarization upon metal coordination, implying that the absorption feature in TUS 8 is a consequence of linker-to-metal coordination interactions rather than mere physical mixture of components. This interpretation is further supported by solid-state UV–Vis spectroscopy, where TUS 8 displays a bathochromically shifted band at 232 nm, in contrast to 221 nm for the SDI linker (Fig. S13). The observed red shift in the solid state likely arises from enhanced π-delocalization and intercluster electronic communication facilitated by the planar, conjugated SDI bridges and argentophilic Ag⋯Ag interactions within the 2D network. Photoluminescence studies of TUS 8 dispersed in water further reveal a strong emission peak at 344 nm upon excitation at 215 nm (Fig. 5b), indicative of a linker-centered emissive process, possibly with minor contributions from linker-to-metal charge transfer (LMCT). Time-correlated single-photon counting (TCSPC) measurements show that the emission decays monoexponentially with a lifetime of 4.62 ns (Fig. 5c), suggesting a well-defined emissive state with minimal contributions from non-radiative pathways. The relatively long lifetime is attributable to the rigidified cluster–linker architecture, which suppresses vibrational relaxation and enhances radiative recombination. Notably, the presence of argentophilic interactions and the encapsulation of Ag(I) centers within a well-passivated ligand shell mitigate quenching pathways commonly associated with open metal sites. Compared to typical photoluminescent SCAMs that often display lifetimes between 1–3 ns,^44,45TUS 8 exhibits a notably longer-lived excited state, placing it among the more efficient short-wavelength silver-based emitters. The absolute photoluminescence quantum yield (PLQY) of TUS 8 was determined to be 26.3% (Fig. S15), a notably high value for silver-based cluster materials in aqueous media. This efficiency is a direct consequence of the molecular precision of the Ag₁₂ core, the strongly bound and electronically insulating ligand shell, and the rigid, conjugated framework that restricts nonradiative decay. In TUS 8, the combination of geometric order, argentophilic interactions, and linker-to-metal electronic conjugation yields a synergistic effect that enhances both photophysical stability and luminescence efficiency. Overall, the optical properties of TUS 8 reflect a delicate interplay between the molecular design of the SDI linker, the coordination environment of the Ag(I) centers, and the long-range order of the 2D cluster-assembled framework. The absorption and emission signatures, together with the long lifetime and high quantum yield, underscore the potential of TUS 8 as a robust luminescent platform for sensing applications in aqueous media.

Fig. 5 (a) UV–Vis spectral response of TUS 8 in water; (b) photoluminescence emission spectrum of TUS 8 in water under 215 nm excitation; (c) TCSPC decay curve of TUS 8 recorded at an emission wavelength of 344 nm.

Encouraged by the remarkable luminescence and aqueous stability of TUS 8, we subsequently evaluated its potential as a luminescent sensor for antibiotics in water (Fig. S16). Remarkably, exposure to different antibiotics yielded distinct responses in both emission intensity and wavelength. As illustrated in Fig. 6a, nitrofuran drugs (furazolidone and nitrofurazone), nitroimidazole compounds (ornidazole and dimetridazole), and chloramphenicol all quenched the TUS 8 emission at 344 nm with efficiencies ranging from ∼28% to ∼80%. These particular antibiotics were chosen as representative analytes owing to their clinical relevance, frequent occurrence in environmental monitoring, and their distinct structural and electronic features: nitrofurans are strongly electron-withdrawing, nitroimidazoles contain heteroaromatic moieties capable of π–π and hydrogen-bond interactions, and chloramphenicol incorporates a nitrobenzene functionality with limited conjugation. This diversity enabled systematic evaluation of analyte–framework interactions and provided mechanistic insights into the selective luminescent response of TUS 8. Of these, furazolidone exhibited the largest quenching efficiency (∼79.7%), followed closely by nitrofurazone (∼78.8%), while ornidazole (∼40.7%), dimetridazole (∼34.5%), and chloramphenicol (∼27.8%) displayed more modest effects. Upon incremental addition of antibiotics to aqueous TUS 8 suspensions, photoluminescence titrations (Fig. 6b–f) revealed analyte-dependent modulations in the emission intensity. Beyond quenching magnitude, emission shifts also varied in direction: nitrofuran antibiotics induced a hypsochromic (blue) shift, whereas nitroimidazoles caused bathochromic (red) shifts, with chloramphenicol prompting only a slight red-shift. These divergent behaviors arise from the interplay between analyte electronic structure and framework microenvironment. Nitrofurans, being strongly electron-withdrawing, reduce local polarizability and perturb the conjugated SDI π-system, raising the HOMO–LUMO gap and causing a blue shift. In contrast, nitroimidazoles possess imidazole rings capable of π–π stacking and hydrogen bonding with the SDI linkers, enhancing electronic delocalization and narrowing the energy gap, thereby resulting in a red shift. Chloramphenicol lacks such aromatic interactions and induces only minor perturbation, consistent with a small red shift. Stern–Volmer analysis (I₀/I = K_SV[Q] + 1) was applied to quantify sensitivity (Fig. 7a–d and S17). Linear behavior at low analyte concentrations (up to ∼0.5 mM for nitrofurans; 0.26 mM for nitroimidazoles; 0.38 mM for chloramphenicol) confirms predominance of dynamic quenching, likely via collisional energy transfer or diffusion-mediated contact. Higher analyte levels produced upward-curved plots, indicative of concurrent static quenching (complex formation with the cluster surface), a scenario commonly observed in MOF–analyte interactions. The derived K_SV values (2414.4, 2071.7, 970.3, 776.0, and 167.6 M⁻¹ for furazolidone, nitrofurazone, ornidazole, dimetridazole, and chloramphenicol, respectively) reflect the correlating binding affinity and quenching efficiency. From the linear regions, limits of detection (LODs) were calculated using LOD = 3σ/S (σ = standard deviation of blank; S = slope = K_SV), resulting in LODs of ∼311 μM (furazolidone), 363 μM (nitrofurazone), 775 μM (ornidazole), 969 μM (dimetridazole), and 4485 μM (chloramphenicol). This analytical strategy underscores the sensitivity and selectivity of TUS 8 as a luminescent sensor, particularly for nitrofuran antibiotics. We also evaluated the sensing performance of TUS 8 in tap water to assess its applicability under more practical conditions. The luminescence response profiles in tap water (Fig. S18 and S19) closely mirrored those observed in distilled water, indicating that the presence of common ions and impurities in tap water does not significantly interfere with the selective detection of antibiotics. To assess the contribution of the SDI linker to the overall luminescent behavior, we compared the PL intensity of free SDI in aqueous medium with that of TUS 8 under identical excitation at 215 nm (Fig. S14). While the SDI linker displays only very weak emission, TUS 8 exhibits significantly enhanced and structured photoluminescence, highlighting the crucial role of cluster–linker assembly in activating emissive properties. Furthermore, to evaluate whether SDI alone can function as a sensing unit, we investigated its luminescence response toward representative antibiotics, furazolidone (Fig. S20 and S21) and ornidazole (Fig. S22 and S23). In both cases, the SDI linker showed negligible and non-specific responses, in sharp contrast to the pronounced and selective sensing observed with TUS 8. These results unambiguously establish that the selective luminescent sensing arises from a synergistic interplay between the Ag₁₂ clusters and the SDI linkers within the reticular framework. Recyclability tests further demonstrated the robustness of TUS 8 as a sensor platform. Following sensing experiments with furazolidone and ornidazole, TUS 8 samples were washed and reused over six cycles (Fig. 7e and f), exhibiting negligible loss in quenching efficiency. PXRD patterns of recycled samples remained unchanged (Fig. S24), confirming preservation of crystalline integrity. Element–specific XPS spectra acquired post-furazolidone exposure (Fig. S25) show no significant shifts in binding energies or signal intensities for Ag, S, N, O, or F, indicating preserved oxidation states and coordination environments. Likewise, FT-IR spectra of pristine and post-sensing samples (Fig. S26) retain all characteristic vibrational bands, affirming the chemical stability of SDI linkers and ancillary ligands. These results collectively demonstrate that TUS 8 combines sensitive and analyte-specific luminescence responses with structural durability and reusability, making it a promising candidate for antibiotic detection in aqueous environments.

Fig. 6 (a) Comparative bar chart showing emission attenuation of TUS 8 by various antibiotics. Luminescence response of TUS 8 as a function of concentration for (b) furazolidone, (c) nitrofurazone, (d) ornidazole, (e) dimetridazole, and (f) chloramphenicol.

Fig. 7 Fluorescence quenching plots (Stern–Volmer) of TUS 8 in response to (a) furazolidone, (b) nitrofurazone, (c) ornidazole, (d) dimetridazole, and (e) chloramphenicol in aqueous media. Luminescence response of TUS 8 as a function of concentration for (b) furazolidone. Recyclability performance of TUS 8 in the detection of (e) furazolidone and (f) ornidazole.

Conclusions

In summary, we have successfully synthesized and structurally characterized TUS 8, a robust SCAM based on Ag₁₂ secondary building units and sulfonyldiimidazole linkers. The crystalline framework features a slightly distorted hollow cuboctahedral Ag₁₂ core geometry and exhibits exceptional chemical stability in aqueous environments. Notably, TUS 8 demonstrates efficient ultraviolet-responsive photoluminescence in water, with a high quantum yield of 26.3%, placing it among the most emissive silver-based MOFs reported under similar conditions. This performance arises from the synergistic influence of framework rigidity and argentophilic interactions, which effectively suppress non-radiative decay pathways. Beyond structural and optical merits, TUS 8 operates as a recyclable luminescent probe for the selective detection of various antibiotics in water, exhibiting strong analyte-dependent emission responses and low detection limits. These findings underline the feasibility of integrating atomically precise metal clusters into extended porous networks for real-world sensing applications. Looking forward, this work establishes a strategic foundation for advancing SCAMs as multifunctional platforms in chemical sensing, optoelectronics, and biomedical diagnostics. The demonstrated stability and modularity of TUS 8 open new avenues for designing next-generation luminescent materials that combine molecular precision with environmental resilience, thereby bridging the gap between nanoscale photophysics and macroscopic utility.

Author contributions

S. T., S. D., and Y. N. conceptualized the study and supervised the project. T. I., K. S., and S. T. performed the synthesis. T. I. and K. S. handled the material characterization and application experiments. M. N. and T. K. contributed to the characterization. S. D. wrote the manuscript. All authors contributed to data interpretation and approved the final manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information: the crystallographic data for [Ag₁₂(S^tBu)₆(CF₃COO)₆ (SDI)₄]_n. See DOI: https://doi.org/10.1039/d5nr03351a.

CCDC 2475858 contains the supplementary crystallographic data for this paper.⁵²

Acknowledgements

The authors thank Dr Subhabrata Das (Tanaka Precious Metal Technologies Co., Ltd.) and Jin Sakai (Tokyo University of Science) for their technical assistance. This study was financially supported by the Scientific Research on Innovative Areas “Aquatic Functional Materials” (Grant No. 22H04562), JSPS KAKENHI (Grant No. 23H00289 and 23KK0098), the Yazaki Memorial Foundation for Science and Technology, and the FUSO Innovative Technology Fund.

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Footnote

† These authors contributed equally.

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