TiO2 nanoparticle-Coated 3D-Printed porous monoliths enabling highly sensitive speciation of inorganic Cr, As, and Se

4D-printed programmable sample-/eluent-actuated solid-phase extraction device for trace metal analysis

BACKGROUND

To integrate valves, manifolds, and solid-phase extraction (SPE) columns into a compact device is technically difficult. Four-dimensional printing (4DP) technologies, employing stimuli-responsive materials in three-dimensional printing (3DP), are revolutionizing the fabrication, functionality, and applicability of stimuli-responsive analytical devices that can show time-dependent shape programming to enable more complex geometric designs and functions. However, 4D-printed stimuli-responsive actuators and valves utilized to control flowing streams in SPE applications remain rare. The tunable stimuli-responsive 4D-printed flow control actuators and valves with the capability of the programmable actuation can be used to manipulate flowing streams and simplify the automation of a conventional SPE scheme.

RESULTS

We employed digital light processing three-dimensional printing (3DP), bisphenol A ethoxylate dimethacrylate-based photocurable resins, and 2-carboxyethyl acrylate (CEA)-incorporated flexible photocurable resins to fabricate an SPE column positioned between two [H+]-responsive flow-actuated needle valves. The two valves sequentially close after loading an alkaline sample (pH > pKa of CEA) due to swelling of the stem. Subsequently, they sequentially open upon loading an acidic eluent (pH < pKa of CEA; deswelling of the stem). The optimized device enabled a semi-automatic SPE scheme for Mn, Co, Ni, Cu, Zn, Cd, and Pb ions and showed competitive performance when coupled with inductively coupled plasma mass spectrometry-with the method detection limits ranging from 0.5 to 5.9 ng L-1. We validated the reliability and applicability of this method by analyzing the metal ions in reference materials (CASS-4, SLRS-5, 1643f, and Trace Elements Urine L-2) and spike analyses of natural water and human urine samples.

SIGNIFICANCE

To the best of our knowledge, our device is the first demonstration of an SPE scheme performed by the programmable actuation of 4D-printed stimuli-responsive flow control valves, highlighting the analytical applicability of the tunable stimuli-responsive 4D-printed parts and the promising capability of 4DP technologies in advancing conventional sample pretreatment devices.

Fully 4D-Printed Near-Infrared-Actuated Lab-on-Valve Solid-Phase Extraction Devices

Four-dimensional printing (4DP) technologies can expand the functionality of stimuli-responsive devices to enable the integration of multiple stimuli-responsive parts into a compact device. Herein, we used digital light processing three-dimensional printing technique, flexible photocurable resins, and photocurable resins of the temperature-responsive hydrogels comprising N-isopropylacrylamide (NIPAM), N,N'-methylenebis(acrylamide) (MBA), and graphene for 4DP of a lab-on-valve (LOV) solid-phase extraction (SPE) device. This device featured flow manifolds and a monolithic packing connected by four near-infrared (NIR)-actuated temperature-responsive switching valves composed of a poly(NIPAM/MBA) (PNM) ball pushing a flexible membrane. NIR irradiation caused the deswelling of the PNM ball [temperature > volume phase transition temperature (VPTT) of the hydrogel], and the valve was opened to switch the flow direction. The termination of this irradiation caused the swelling of the PNM ball (temperature < VPTT of the hydrogel) to close the valve and thus recover the original flow direction to achieve the automatic NIR-actuated fluid control. The optimized 4D-printed NIR-actuated LOV-SPE device enabled a fully automatic SPE scheme coupled with inductively coupled plasma mass spectrometry for the determination of Mn, Co, Ni, Cu, Zn, Cd, and Pb ions (detection limits = 0.1,6.8 ng L-1). The reliability of this analytical method was validated by determining the metal ions in the four reference materials (CASS-6, SLRS-5, 1643f, and Trace Elements Urine L-2) and environmental water and human urine samples. Our results demonstrated the capability and applicability of 4DP technologies for advancing the automation of LOV-SPE schemes and related analytical methods.

3D-printed thermally expanded monolithic foam for solid-phase extraction of multiple trace metals

Digital light processing (DLP) 3DP, commercial acrylate-based photocurable resins, and thermally expandable microspheres-incorporated flexible photocurable resins were employed to fabricate an SPE column with a thermally expanded monolithic foam for extracting Mn, Co, Ni, Cu, Zn, Cd, and Pb ions prior to the determination using inductively coupled plasma mass spectrometry. After optimization of the thermally activated foaming, the design and fabrication of the SPE column, and the automatic analytical system, the DLP 3D-printed SPE column with the thermally expanded monolithic foam extracted the metal ions with up to 14.8-fold enhancement (relative to that without incorporating the microspheres), with absolute extraction efficiencies all higher than 95.6%, and method detection limits in the range from 0.5 to 5.2 ng L-1. We validated the reliability and applicability of this method by determination of the metal ions in several reference materials (CASS-4, SLRS-5, 1643f, and Seronorm Trace Elements Urine L-2) and spiked seawater, river water, ground water, and human urine samples. The results illustrated that to incorporate the thermally expandable microspheres into the photocurable resins with a post-printing heating treatment enabled the DLP 3D-printed thermally expanded monolithic foam to substantially improve the extraction of the metal ions, thereby extending the applicability of SPE devices fabricated by vat photopolymerization 3DP techniques.

One-pot preparation of magnetic composite containing boronic acid groups and aminated multwalled carbon nanotubes for the speciation of Se(IV) and Se(VI) in water and milk samples by combination with chromatographic quantification

Speciation of Se(IV) and Se(VI) is essential due to their significant differences in reactivity, toxicity and bioavailability. Efficient extraction is the pivotal step in the quantification of inorganic selenium species. In this work, a new magnetic nano-composite (MNC) containing boronic acid group and aminated multwalled carbon nanotubes was facilely fabricated by means of one-pot hydrothermal strategy. The prepared MNC contained abundant functional groups and satisfactory magnetic saturation value. Combining with magnetic solid phase extraction (MSPE) format, the MNC displayed satisfactory capture performance towards the complex formed by the coordination of Se(IV) and o-phenylenediamine (OPA). Adsorption isotherm and adsorption kinetics were studied in detail to investigate the adsorption procedure of Se(IV)/OPA complex on MNC. Under the optimal preparation conditions of MNC and extraction parameters, the MNC/MSPE was connected with HPLC equipped with a diode array detector (DAD) to quantify trace Se(IV) and Se(VI) species in water and milk samples. Se(VI) was reduced to Se(IV) and then the total inorganic Se was quantified by the developed method. Subtraction method was used to measure the concentration of Se(VI). The achieved limits of detection were in the ranges of 0.0082-0.013 μg/L and 0.041-0.13 μg/kg for water and milk samples, respectively. Recoveries in actual samples spiked with different amounts of analytes varied from 81.0 % and 117 %, and the RSDs for repeatability varied from 1.0 % to 10 %. In comparison with existing studies based on MSPE, the established method presents some merits such as greenness in the preparation of magnetic adsorbent, rapid extraction procedure, low cost and satisfactory sensitivity in the speciation of inorganic Se species.

4D-Printed Elution-Peak-Guided Dual-Responsive Monolithic Packing for the Solid-Phase Extraction of Metal Ions

Four-dimensional printing (4DP) technologies are revolutionizing the fabrication of stimuli-responsive devices. To advance the analytical performance of conventional solid-phase extraction (SPE) devices using 4DP technology, in this study, we employed N-isopropylacrylamide (NIPAM)-incorporated photocurable resins and digital light processing three-dimensional printing to fabricate an SPE column with a [H+]/temperature dual-responsive monolithic packing stacked as interlacing cuboids to extract Mn, Co, Ni, Cu, Zn, Cd, and Pb ions. When these metal ions were eluted using 0.5% HNO3 solution as the eluent at a temperature below the lower critical solution temperature of polyNIPAM, the monolithic packing swelled owing to its hydrophilic/hydrophobic transition and electrostatic repulsion among the protonated units of polyNIPAM. These effects resulted in smaller interstitial volumes among these interlacing cuboids and improvements in the elution peak profiles of the metal ions, which, in turn, demonstrated the reduced method detection limits (MDLs; range, 0.2-7.2 ng L-1) during analysis using inductively coupled plasma mass spectrometry. We studied the effects of optimizing the elution peak profiles of the metal ions on the analytical performance of this method and validated its reliability and applicability by analyzing the metal ions in reference materials (CASS-4, SLRS-5, 1643f, and Seronorm Trace Elements Urine L-2) and performing spike analyses of seawater, groundwater, river water, and human urine samples. Our results suggest that this 4D-printed elution-peak-guided dual-responsive monolithic packing enables lower MDLs when packed in an SPE column to facilitate the analyses of the metal ions in complex real samples.