“Inorg. Chem.” A Stable Zinc(II) Metal–Organic Framework: Turn-On Blue-Shift Fluorescent Sensor for the Detection of Amino Acids and Pyridine-2,6-Dicarboxylic Acid in Living Cells, and Its Application in Aerosol Jet Printing
Product Introduction
Equipment Parameters
I. Core Research Abstract
Ultra-wide pH-stable three-dimensional MOF crystals
JXUST-53 features a unique five‑zinc cluster–based secondary structural motif; its crystal structure remains intact after 24 hours of immersion in pH 1–12 acidic–alkaline solutions and various organic solvents, and it exhibits a thermal decomposition temperature as high as 330°C, demonstrating chemical stability far superior to that of conventional fluorescent MOFs.
Specifically activated blue-shifted fluorescence for multiplexed target recognition
It enables MOF‑based probe‑specific detection of threonine (L‑Thr); simultaneously, it accurately distinguishes histidine (L‑His) and the anthrax biomarker DPA. Upon addition of the target analyte, fluorescence is markedly enhanced with a blue shift, while more than ten other amino acids remain unaffected, demonstrating excellent resistance to coexisting interferents.
- The detection limit for L-Thr is 1.323 μM; for L-His, it is 0.587 μM; and for DPA, it is as low as 0.107 μM, significantly below the threshold concentration associated with anthrax infection.
- The DPA system exhibits an 11-fold increase in fluorescence intensity, with a visible green-to-blue color change under UV illumination, making it suitable for rapid naked-eye screening.
Low-toxicity biocompatibility, in situ fluorescence imaging of living cells
MCF-7 tumor cells were incubated for 24 hours at a concentration of 25 μM, yielding a cell viability exceeding 90%. The probe can autonomously enter the cells, and intracellular L-His, L-Thr, and DPA all generate distinct blue-shifted fluorescence signals, enabling in vivo visualization and tracking of endogenous biomarkers.
Aerosol-jet digital printing of MOF fluorescent sensing patterns
JXUST-53 ethanol‑based dispersion ink is compatible with ultrasonic atomization aerosol‑printing technology, enabling low‑temperature (60°C) substrate patterning and the printing of custom fine‑scale designs (such as institutional logos). After immersion in a DPA solution, the fluorescent color of the pattern undergoes a visible change, allowing the material to be fabricated into a disposable, visual‑readout detection chip.
Recyclable and Reusable Sensing System
After multiple ethanol elutions for regeneration, the fluorescence response showed no significant decay over five consecutive cycles, and the crystal structure remained intact, enabling the probe to be reused and reducing the cost of detection consumables.
II. Aerosol Jetting Fabrication Process and Core Process Advantages
(1) Complete AJP Printing Process for MOF Sensing Films
- JXUST-53 crystalline powder is ultrasonically dispersed in anhydrous ethanol to prepare a stable MOF‑based printing ink.
- The aerosol ultrasonic atomization module disperses the ink, with a carrier gas flow of 80 sccm and a sheath gas flow of 100 sccm, working in concert to focus the micro‑aerosol beam.
- The nozzle is positioned 4 mm from the glass substrate, and the build platform is maintained at a constant temperature of 60°C. Printing is performed at a low speed, layer by layer (with 10 layers stacked to form the final structure).
- The solvent evaporates naturally at room temperature, yielding a uniform MOF fluorescent sensing pattern with well-defined edges.
- Under UV illumination, a visual sample‑identification test is performed; the device can be cut into a portable test strip.
(II) Five Core Processes (in comparison with spin coating, blade coating, and screen printing)
- Maskless direct writing of arbitrarily fine patterns
CAD allows for custom sensor labeling, array configuration, and partitioned detection zones, with a minimum printing resolution of 10 μm. Spin coating, by contrast, can only apply a uniform coating across the entire substrate and cannot achieve patterned, structured sensing.
- Low-temperature, mild processing preserves the MOF’s fluorescent structure.
The entire process employs low-temperature substrate drying at 60°C, with no high-temperature sintering, thereby preventing thermal decomposition of the MOF coordination framework and fully preserving its open‑framework fluorescence response.
- The ink exhibits excellent compatibility, and the MOF suspension enables stable atomization.
Ethanol-based, low-viscosity MOF dispersion inks enable long‑term continuous printing without nozzle clogging, produce films of uniform thickness, and deliver consistent fluorescence signals across the entire area.
- Non-contact conformal deposition, compatible with both rigid and flexible substrates.
Glass, PET, and other substrates can all be directly printed, with potential for future applications such as medical flexible test strips and site-specific functionalization of sensing regions within microfluidic chips.
- High consumable utilization and on-demand localized deposition.
Only the detection area is coated with MOF material, while the full‑sheet lamination process results in substantial waste of crystalline powder, significantly reducing the cost of using high‑end MOF probes.
III. Five Key Technological Innovations
Innovation 1: A novel pH-stable Zn-MOF, enabling the innovative preparation of a threonine-specific fluorescent probe.
Innovation 2: Photoinduced Electron Transfer (PET) + Absorption-Enhanced Dual-Sensing Mechanism
Innovative 3-AJP aerosol-integrated visualization MOF sensing thin-film process
Innovative 4-cell-compatible MOF probes enable in situ imaging of intracellular biomarkers.
Innovation: A versatile multi‑scenario detection platform—solution quantification, cell imaging, and portable test strips.
IV. Existing Challenges in Processes and Materials and Corresponding Solutions for Overcoming Them
Challenge 1: Most fluorescent MOFs collapse in acidic or basic environments, precluding their use for analyzing complex biological samples.
Challenge 2: Conventional film-forming processes involve coating the entire surface, making it impossible to fabricate partitioned, visualizable sensing markers.
Challenge 3: Conventional fluorescent probes exhibit high cytotoxicity, making in situ detection in living cells difficult.
Challenge 4: MOF powders tend to agglomerate, and conventional printing often results in non-uniform fluorescence in the resulting thin films.
Challenge 5: Most fluorescent probes are single-use, resulting in high detection costs.
V. Future Diversified Industrial Application Scenarios
1. Public Health Anthrax Rapid On-Site Screening Test Strip
2. Non-invasive clinical screening chip for amino acids in body fluids
3. Imaging Consumables for Cell Biology Laboratories
4. Site-specific sensing modification of microfluidic organ-on-a-chip devices
5. Fluorescent teaching aids for visualizing instruction and research, along with anti-counterfeiting films
Figure 1. (a) The coordination environment of Zn(II) ions and the linking modes of the organic ligands in JXUST‑53; (b) the three-dimensional structure of JXUST‑53; (c) the topological structure of JXUST‑53.
Figure 2. Fluorescence emission spectra after detection of different amino acids (Inset: Image of JXUST‑53 dispersed in ethanol solutions containing L‑threonine or L‑histidine, excited under a 365 nm UV lamp).
Figure 3. XPS spectra of the O 1s and Zn 2p levels before and after JXUST‑53 recognition: (a, c) L‑Thr; (b, d) L‑His.
Figure 4. (a) Singlet–singlet energy transfer process among H4BTDI, L-Thr, and L-His; (b) Calculated HOMO and LUMO energy levels of H4BTDI, L-Thr, and L-His.
Figure 5. Fluorescence emission spectra of JXUST‑53 in the presence of various interfering substances (Inset: image of JXUST‑53 dispersed in an ethanol solution containing DPA, excited under a 365 nm UV lamp).
Figure 6. (a) XPS spectra of the O 1s orbital before and after DPA recognition by JXUST‑53; (b) XPS spectra of the Zn 2p orbital before and after DPA recognition by JXUST‑53.
Figure 7. (a1–d1) are bright-field transmission images of JXUST‑53, JXUST‑53@DPA, JXUST‑53@L‑Thr, and JXUST‑53@L‑His, respectively; (a2–d2) are fluorescence field images of the same samples, respectively; and (a3–d3) are overlay field images of the corresponding samples.
Figure 8. (a) Schematic diagram of the aerosol jet printing process on a heated substrate; (b) Photograph of a glass plate bearing the university logo, printed using the JXUST‑53 device via AJP and illuminated with a 365 nm UV lamp; (c) Photograph of a glass plate bearing the university logo, printed using the JXUST‑53 device via AJP, with the glass plate immersed in a DPA solution and illuminated with a 365 nm UV lamp.
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