In modern analytical chemistry researchers pursue novel materials to meet analytical challenges such as improvements in sensitivity, selectivity, and detection limit. Metal-organic frameworks (MOFs) are an emerging class of microporous materials, and their unusual properties such as high surface area, good thermal stability, uniform structured nanoscale cavities, and the availability of in-pore functionality and outer-surface modification are attractive for diverse analytical applications. This Account summarizes our research on the analytical applications of MOFs ranging from sampling to chromatographic separation. MOFs have been either directly used or engineered to meet the demands of various analytical applications. Bulk MOFs with microsized crystals are convenient sorbents for direct application to in-field sampling and solid-phase extraction. Quartz tubes packed with MOF-5 have shown excellent stability, adsorption efficiency, and reproducibility for in-field sampling and trapping of atmospheric formaldehyde. The 2D copper(II) isonicotinate packed microcolumn has demonstrated large enhancement factors and good shape- and size-selectivity when applied to on-line solid-phase extraction of polycyclic aromatic hydrocarbons in water samples. We have explored the molecular sieving effect of MOFs for the efficient enrichment of peptides with simultaneous exclusion of proteins from biological fluids. These results show promise for the future of MOFs in peptidomics research. Moreover, nanosized MOFs and engineered thin films of MOFs are promising materials as novel coatings for solid-phase microextraction. We have developed an in situ hydrothermal growth approach to fabricate thin films of MOF-199 on etched stainless steel wire for solid-phase microextraction of volatile benzene homologues with large enhancement factors and wide linearity. Their high thermal stability and easy-to-engineer nanocrystals make MOFs attractive as new stationary phases to fabricate MOF-coated capillaries for high-resolution gas chromatography (GC). We have explored a dynamic coating approach to fabricate a MOF-coated capillary for the GC separation of important raw chemicals and persistent organic pollutants with high resolution and excellent selectivity. We have combined a MOF-coated fiber for solid-phase microextraction with a MOF-coated capillary for GC separation, which provides an effective MOF-based tandem molecular sieve platform for selective microextraction and high-resolution GC separation of target analytes in complex samples. Microsized MOFs with good solvent stability are attractive stationary phases for high-performance liquid chromatography (HPLC). These materials have shown high resolution and good selectivity and reproducibility in both the normal-phase HPLC separation of fullerenes and substituted aromatics on MIL-101 packed columns and position isomers on a MIL-53(Al) packed column and the reversed-phase HPLC separation of a wide range of analytes from nonpolar to polar and acidic to basic solutes. Despite the above ...

A zeolitic imidazolate framework-8 (ZIF-8) nanocrystal coated capillary is shown not only to have a strong ability to sieve branched alkanes from linear alkane isomers owing to the narrow pore windows but also to offer excellent features for high-resolution gas chromatographic separation of linear alkanes due to van der Waals interaction between linear alkanes and the hydrophobic inner surfaces of the micropores. This makes the ZIF-8 coated capillary very promising for the specific adsorption and separation of alkanes in complicated matrices.

Metal-organic frameworks (MOFs) were employed to design tandem molecular sieves as a dual platform for selective solid-phase microextraction (SPME) and high-resolution gas chromatographic (GC) separation of target analytes in complex matrixes. An elegant combination of a ZIF-8-coated fiber for SPME with a ZIF-8-coated capillary for GC allows selective extraction and separation of n-alkanes from complex matrixes such as petroleum-based fuel and biological fluids. The proposed tandem ZIF-8 molecular sieves not only offered good enhancement factors from 235 (hexane) to 1212 (nonane), but also exhibited wide linearity with 3 orders of magnitude for the tested linear alkanes. The limits of detection for the linear alkanes ranged from 0.46 ng L(-1) (nonane) to 1.06 ng L(-1)(hexane). The relative standard deviations of retention time, peak area, peak height, and half peak width for five replicate determinations of the tested n-alkanes at 30 ng L(-1) were 0.02-0.26%, 1.9-8.6%, 1.4-6.0%, and 1.3-7.2%, respectively. The developed tandem ZIF-8 molecular sieves were further used for the determination of linear alkanes in petroleum-based fuel and human serum. The large diversity in structure and pore size allows various combinations of MOFs for designing an MOF-based tandem molecular sieve platform to achieve different selectivities in extraction and chromatographic separation and to solve headache problems in complex real sample analysis.

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ObjectiveThree-dimensional (3D) printing is a recent technological development that may play a significant role in orthodontic diagnosis and treatment. It can be used to fabricate skull models or study models, as well as to make replica teeth in autotransplantation or tooth impaction cases. The aim of this study was to evaluate the accuracy of fabrication of replica teeth made by two types of 3D printing technologies.MethodsFifty extracted molar teeth were selected as samples. They were scanned to generate high-resolution 3D surface model stereolithography files. These files were converted into physical models using two types of 3D printing technologies: Fused deposition modeling (FDM) and PolyJet technology. All replica teeth were scanned and 3D images generated. Computer software compared the replica teeth to the original teeth with linear measurements, volumetric measurements, and mean deviation measurements with best-fit alignment. Paired t-tests were used to statistically analyze the measurements.ResultsMost measurements of teeth formed using FDM tended to be slightly smaller, while those of the PolyJet replicas tended to be slightly larger, than those of the extracted teeth. Mean deviation measurements with best-fit alignment of FDM and PolyJet group were 0.047 mm and 0.038 mm, respectively. Although there were statistically significant differences, they were regarded as clinically insignificant.ConclusionsThis study confirms that FDM and PolyJet technologies are accurate enough to be usable in orthodontic diagnosis and treatment.

Upconversion nanocrystals (UCNCs) hold promise for bioimaging, solar cells, photocatalysis and volumetric displays. However, their upconversion luminescence intensities are usually low due to the weak and narrowband near-infrared absorption of lanthanide ions. Herein, we introduce and validate a strategy to hugely enhance upconversion luminescence intensity by using an organic near-infrared dye as an antenna to sensitize core/shell UCNCs. The dye can increase absorptivity and broaden the absorption spectrum of the UCNCs. Such dye sensitization, in combination with a core/shell structure, can tremendously enhance the upconversion luminescence (UCL) intensity of the UCNCs. The UCL intensity of dye-sensitized UCNCs excited at 820 nm is 800-folds higher than that of pure UCNCs excited at 980 nm. Further enhancement can be obtained by optimization of the dye emission and UCNC absorption spectral overlap. Moreover, the proposed approach can be extended to cover any part of the solar spectrum by using a set of dyes. This work provides new insights into the efficient enhancement of upconversion luminescence of the UCNCs and facilitates their applications.

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