Technology Report pubs.acs.org/jchemeduc
Simple and Inexpensive 3D Printed Filter Fluorometer Designs: UserFriendly Instrument Models for Laboratory Learning and Outreach Activities Lon A. Porter, Jr.,* Cole A. Chapman, and Jacob A. Alaniz Department of Chemistry, Wabash College, Crawfordsville, Indiana 47933, United States S Supporting Information *
ABSTRACT: In this work, a versatile and user-friendly selection of stereolithography (STL) files and computer-aided design (CAD) models are shared to assist educators and students in the production of simple and inexpensive 3D printed filter fluorometer instruments. These devices are effective resources for supporting active learners in the exploration of instrument design and performance. In contrast to sophisticated commercial-grade fluorometers, the models provided here are open source, customizable for a variety of applications, and easily assembled by students in activities that directly confront the “black box” perception of analytical instrumentation. In order to aid beginner CAD and 3D printer users, these models are compatible with accessible software packages, such as 123D Design and Inventor Professional. Additionally, CAD tutorials and extensive slicer settings are supplied to assist educators and students in modifying digital designs and obtaining reliable 3D prints. The provided filter fluorometer models are printed quickly, consume about a dollar’s worth of plastic, and do not require complex support structures when 3D printed. Once fabricated and assembled, these devices perform well in a range of laboratory activities, including the quantitative determination of luminescent analytes at the ppm or ppb level. KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Second-Year Undergraduate, Analytical Chemistry, Public Understanding/Outreach, Hands-On Learning/Manipulatives, Instrumental Methods, Laboratory Equipment/Apparatus, Quantitative Analysis, Spectroscopy
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INTRODUCTION Fluorescence techniques serve as powerful analytical methods for elucidating important chemical, biochemical, and biological phenomena. Luminescent probes and innovative labeling strategies allow for protein detection, investigation of lipid dynamics, and tracking of cellular processes, among others.1 Beyond these significant applications, fluorescence remains an important subject in the undergraduate chemistry curriculum as a fundamental excitation−emission process.2 These topics are most effectively explored in the laboratory, where students are challenged to investigate complex phenomena within an applied and relevant context. However, the prohibitive cost of research-grade instrumentation restricts the infrastructure available for laboratory learning activities. While few, previous articles have described portable filter fluorometers for student use.3−6 These devices are near-commercial in appearance and operation. While they are effective analytical tools, instruments of this type require intricate assemblies, employ complex circuitry, and are encased in a way that hides away important components. As with many modern instruments that feature the convenience of “push-button” data acquisition, significant and fundamental aspects of student learning are lost. In an effort to directly confront this “black box” perception of instrumentation, the filter fluorometer designs shared here © XXXX American Chemical Society and Division of Chemical Education, Inc.
purposely make major components accessible and are easily assembled by students during laboratory activities. The simple models presented provide an effective entry point for student design and construction of functional instrumentation. These introductory tools are meant to support discovery learning related to the technology and fundamental principles of analysis.7 In this way, students explore instrumental design directly and participate in active learning exercises related to excitation source selection, filter choice, and simple circuit building during assembly and data acquisition. In order to assist educators and students in the fabrication of simple and inexpensive 3D printed filter fluorometer instruments, a versatile and user-friendly selection of computer-aided design (CAD) models and stereolithography (STL) files are shared in this report (Figure 1). These instrument files provide a convenient and customizable starting point in developing purpose-built devices for use in fluorescence-based analytical laboratory activities and outreach projects. Increased access to consumer-grade 3D printers via university fabrication centers and community maker spaces provides exciting opportunities Received: July 4, 2016 Revised: November 5, 2016
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Figure 1. (a) Example multipart CAD model assembly rendering for a filter fluorometer instrument. (b) Complete filter fluorometer design fabricated via 3D printing using polylactic acid (PLA) plastic. Both LED source (left) and CdS photocell (right) are displayed after mounting in 3D printed docks. (c) Simplified wiring diagram with LED (left) and detector (right) dock inserted, shown alongside an assembled and fully functional filter fluorometer. (d) In order to reduce the required number of 3D printed components for novice users, the alternate design shown here employs rubber stopper source and detector mounts in place of the 3D printed docks.
consume about a dollar’s worth of plastic, and may be printed without any complex support structures. While the time required to print the instruments shared here is minimal, it is still not feasible to both fabricate the devices and use them within a typical laboratory period. Therefore, the 3D printed filter fluorometers should be printed and collected into kits before use in laboratory and outreach activities. However, the opportunity to engage in digital design, customization, and 3D printing might warrant a separate laboratory or activity period. Once assembled by students, these devices perform well in a variety of laboratory activities, including the quantitative determination of luminescent analytes at the ppm or ppb level.
for educators and students to create innovative new learning tools. Recent examples include designs for visualizing molecular models,8 symmetry elements,9 and potential energy surfaces,10 among others. However, while CAD and 3D printing are increasingly employed in the customization and design of research-grade analytical instrumentation,11 few previous efforts have focused on applying this versatile technology in the development of new educational tools for student laboratory learning.12−15 Three-dimensional printing offers a powerful and precise alternative to instruments produced from shoeboxes and other household items. It represents a fundamentally new fabrication paradigm for engaging educators and students in the production of inexpensive and customizable analytical tools via deliberate digital design. This new technology transcends the limitations of conventional tooling and grants access to customized analytical devices for exploring activities and fundamental concepts inaccessible to more conventional instruments. However, 3D printing equipment and CAD software are often associated with a steep learning curve that presents a barrier to entry for novice users. Similarly, the myriad settings associated with converting stereolithography (STL) files into the G-code files required for reliable 3D printing provide yet another hurdle. In order to assist beginner CAD and 3D printer users, the designs reported are compatible with accessible software packages, such as 123D Design and Inventor Professional. Several step-by-step CAD tutorials are presented in the Supporting Information with notes on how users might customize the instruments reported here. Additionally, extensive slicer settings are supplied in the Supporting Information to help educators and students in obtaining consistent 3D prints. The majority of the provided filter fluorometer models require approximately 3 h of print time,
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DESIGN AND ASSEMBLY Building upon on our previous work in developing simple 3D printed colorimeters,13 the filter fluorometer models reported here were designed to provide students with hands-on opportunities to explore fundamental spectroscopic principles and instrument performance via quantitative analysis experiments. However, these instrument designs are also suitable for investigating chemical kinetics, fluorescence quenching, and a host of other significant applications. The devices shared here have been successfully used in Wabash College laboratory coursework and are appropriate for high school and outreach activities. These 3D printed filter fluorometers are provided to students in the form of an unassembled kit when used as part of both verification and inquiry-based experiments. Kit components include the 3D printed instrument body, optical filters if required, circuit components (e.g., batteries, resistors, LED source, phototransistor detector, and alligator clip leads), and an inexpensive digital multimeter. A detailed list of materials and commercial sources is provided in the Supporting Information. An entire filter fluorometer instrument, including B
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optical filter, digital multimeter, and batteries, can be obtained for less than $50, which presents a significant savings when compared to commercial instruments. The inexpensive nature of the instrument design provides the opportunity for each student laboratory partnership or group to utilize a 3D printed filter fluorometer for the entire activity period. This is in contrast to typical models of student engagement with fluorometry activities, where one instrument must serve an entire class of students. It also increases the possibility of introducing fluorescence-based experiments into high school, introductory undergraduate, and courses intended for nonmajors. Similarly, advanced level analytical, physical, and biochemistry courses may adapt the instrument models presented here to activities appropriate for more in-depth explorations of relevant fundamental content and applications. Enhanced engagement via active learning strategies involving student construction of functional instrumentation is an effective way to assist learners in discovering the technology and fundamental principles of analysis. The precision, flexibility, and cost savings offered through the combination of CAD and 3D printing empowers educators and students to fabricate customized analytical tools for exploring a variety of concepts and analytical applications. In a departure from conventional filter fluorometer designs, the 3D printed instrument models described here purposefully avoid case-styled enclosures, circuit boards with complex electronics, and expensive optical components. Instead, all of the major electrical components remain exposed and are easily accessed by students during assembly and use. The single-piece, 3D printed instrument body was modeled to provide a simple, stable, and durable design (Figure 1a) that prints quickly and takes up minimal bench space. While quartz sample cells are recommended, the device is compatible with the glass and plastic cuvettes more frequently encountered in the introductory undergraduate and high school laboratory. Digital design affords a great deal of flexibility for quick and simple alterations to accommodate any variety of cell geometries. For example, an alternate filter fluorometer model is displayed in Figure 2b that contains a cylindrical sample housing for use of 1/2 in. diameter glass test tube cells. A variety of additional CAD designs are provided in the Supporting Information. The excitation and emission light path arms are oriented 90° to each other in order to reduce the amount of scattered LED excitation light from reaching the detector (Figure 1b). Each arm may incorporate a capped optical filter housing that is compatible with a wide range of glass or plastic filters. Using simple CAD alterations, these housings may be adapted for circular, square, or almost any optical filter geometry. Docking ports terminate the light path arms, facilitating simple insertion and alignment of the excitation source and detector. This modular configuration allows for the incorporation of a wide variety of LEDs and solid-state detector choices. A simple rectangular cap secures each end-cap dock in place during use (Figure 1c). Alternatively, source and detector elements may be held in place using size 000 rubber stoppers so that the number of 3D printed parts required is reduced (Figure 1d). Both arrangements result in a secure fit that provides a consistent alignment and prevents gaps that might allow stray light to enter the instrument. The simple geometry of the design minimizes the plastic required for printing, thereby reducing printing time. It also avoids any overhang features that require 3D printer software generated support scaffolds. These support
Figure 2. (a) Absorption spectrum of 5.00 ppm aqueous sodium fluorescein with an overlay of the normalized emission spectra for violet (370 nm), indigo (405 nm), blue (465 nm), and green (525 nm) LEDs. Absorbance data was acquired using a PerkinElmer Lambda 40 UV−vis spectrophotometer and emission spectra were obtained using an Ocean Optics USB-650 spectrometer. (b) 3D printed filter fluorometers for use with cuvette (left) and test tube (right) sample cells are shown here with caps, LED source, and a photocell detector. (c) Standard calibration curves obtained for fluorescein using a 465 nm LED source, 495 nm cutoff filter, and CdS photocell detector employing 3D printed filter fluorometer designs for use with a (●) cuvette and (■) test tube sample cell.
structures often complicate fabrication and prove difficult for some software packages. Instructions for instrument preparation, operation, and a simple wiring diagram are provided in the Supporting Information. While more sophisticated electronics may be adapted to enhance instrument performance for advanced students, two simple voltage divider circuits are employed for introductory-level applications (Figure 1c). Similarly, alligator clip connectors avoid the need for soldering and allow for facile assembly and troubleshooting during use. This open design leaves major components of the instrument exposed in an effort to avoid the “black box” perception of instrumentation. In addition to wiring diagrams, instructors may supply students with prelaboratory data, such as analyte excitation and emission C
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analyte. Advances in semiconductor fabrication have yielded a great variety of commercially available LEDs. While these inexpensive light sources are versatile, it is important to recognize that they are not tunable. Thus, students should take care to select an LED source with greatest emission intensity near the analyte absorption maximum. Figure 2a displays the emission spectra for several LED sources superimposed onto the visible absorbance spectrum for aqueous sodium fluorescein. Of the available LEDs available to the students, discussion should arrive at the conclusion that the blue (465 nm) LED best matches the excitation spectrum for fluorescein. This LED source results in the most appropriate choice of excitation source for the instrument design. When possible, similar discussions may be prompted to focus on optical filter selection for excitation and emission, as well as solid-state detector choice. The 3D printed filter fluorometers are well-suited for introductory quantitative analysis activities. These simple and inexpensive instrument designs are both sensitive and adaptable for a wide range of laboratory learning applications. Standard calibration curves for aqueous sodium fluorescein (D&C Yellow #8) are shown in Figure 2c. Fluorescein is widely used in fluorescence labeling methodologies and often employed in undergraduate laboratory activities due to its stability and high quantum yield. Data was collected using a high-power 465 nm LED (∼20 mW), quartz cuvette, and CdS detector. While glass filters are optional, an emission cutoff filter (495 nm) is suggested for best results. Information on these components, along with sourcing and pricing, is provided in the Supporting Information. The calibration curve yielded a linear fit from 1.8 to 108 ppb. Increasing sample concentrations beyond this range resulted in increasingly significant deviations from linearity. While quartz and glass cuvettes produced the most accurate results, inexpensive glass test tube sample cells are often preferred for outreach activities or when a large number of students must be accommodated. The plots shown in Figure 2c demonstrate that both 3D printed filter fluorometer sample configurations resulted in linear standard calibration curves for fluorescein. Figure 3a displays both the excitation and emission spectra for dilute aqueous solutions of tris(2,2′-bipyridine)ruthenium(II) chloride. This complex is an excellent choice for exploring the quantitative determination of metal species and is also used in fluorescence-based thermal imaging. As in the case of fluorescein above, providing excitation and emission spectra to students encourages active engagement in the determination of instrument configuration and operation. The ability to modify digital designs to produce adaptable devices is a testament to the power of rapid prototyping made possible by modern 3D printing technology. The filter fluorometer CAD models provided here may be easily customized as needed for student use. Instrument variants shown in Figure 3b display devices incorporating zero, one, or two optical filters. Filter selection provides a simple, yet important opportunity to engage active learners. While small tungsten and halogen sources may be used, the emission spectra of high-quality LED excitation sources is often narrow enough to preclude the use of low-cost bandpass excitation filters. Most economy-grade optical glass filters contain transmission bands that are wider than the emission spectra of quality LEDs. Although narrow bandpass filters (±10 nm) may be purchased, the limited increase in performance often fails to justify the increased cost of these filters. However, the large Stokes shift exhibited by [Ru(bpy)3]-
spectra, so that lab groups are challenged with selecting appropriate LED source, optical filter, and solid-state detector choices during assembly. This provides the opportunity to employ inquiry-based learning experiences as an alternative to simple verification approaches. While each circuit may be powered by a separate 9 V battery for field locations, inexpensive ac to dc power supplies were found to be more stable, convenient, and sustainable options for use in the typical laboratory setting. The 3D printed filter fluorometers shared here are compatible with a wide range of commercially available LEDs that offer low-voltage, long-lived, and inexpensive light sources. These light sources are available for a wide range of visible and ultraviolet wavelengths, allowing for analysis of a diverse range of substances. While several solid-state detectors may be employed, simple and inexpensive cadmium sulfide (CdS) photocells proved to offer reliable performance. The significant flexibility offered by CAD and 3D printing allows educators and students the ability to enlarge or reshape the instrument design in order to accommodate any number of source, detector, or optical filter components. Similarly, the provided CAD files may be revised and customized to allow for the integration of lenses to increased performance. While appropriate for advanced students, more complex circuitry may be also incorporated to decrease signal noise, enhance detection limits, and increase sensitivity by inclusion of diodes, capacitors, and amplifiers, as desired.
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OPERATION AND PERFORMANCE Following assembly, collection of quality data is simple using the 3D printed filter fluorometer devices described here. Students are provided with an inexpensive digital multimeter to make all voltage measurements. First, a series of voltage readings should be recorded for a cuvette filled with pure solvent (Vreference). Once the average reference voltage is determined, replicate sample measurements (Vsample) are obtained, and the resulting fluorescence signal for each sample is determined via eq 1. Cadmium sulfide photocell detectors require a short time to reach a stable reading at low light levels, so a consistent acquisition delay of about a minute should be maintained for all voltage measurements. Data collected in this way presents an opportunity for students to explore the mathematical power of proper curve fitting for both linear and nonlinear relationships. Similarly, these measurements allow for student determination of appropriate figures of merit for the 3D printed filter fluorometer instrument. While less convenient for unknown determination, nonlinear calibration curves are also worth consideration in exploration of the more general understanding of fluorescence intensity as a function of analyte concentration. fluorescence signal = (Vsample − Vreference)
(1)
When used in inquiry-based activities at the introductory level, students are provided with absorption and emission spectra for the analyte of interest. More advanced students are tasked with obtaining this information directly from the primary literature. Data provided in preparation for the laboratory activity prompts student teams to more effectively engage in formulating an analysis strategy and facilitate much of the instrument design planning. The absorption spectrum should aid in stimulating a student discussion leading to an appropriate LED excitation source selection for a particular D
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Although optical filters may enhance the performance of the 3D printed filter fluorometer and provide an excellent opportunity for illustrating fundamental instrument design principles, they are prohibitively expensive when a greater number of instruments is required for large introductory classes or outreach programs. Acrylic, cellophane, and photographic color filters are less expensive alternatives to glass filters. However, the need for filters is reduced considerably by selecting excitation LED sources that fall outside of the optimal spectral response profile for the CdS photocell detector. Quantitative determination of quinine provides an important example of this strategy. Figure 4a displays standard calibration curves obtained for quinine in 0.05 M H2SO4 using a 370 nm LED excitation source and CdS photocell detector employing 3D printed filter fluorometer designs for use with both excitation bandpass and emission cutoff glass filters, only an emission cutoff filter, and in the absence of any filters. The cost of the 3D printed filter fluorometer kit drops significantly, to below $30, in the absence of glass filters. The calibration plots all exhibit a linear response from 0.02 to 4.5 ppm of quinine with comparable sensitivities. This demonstrates that instrument performance is maintained while considerable cost savings are achieved through the elimination of optical filters. Even beyond the linear response range, the calibration curve adheres well to the more general equation for fluorescence intensity, as shown in the Supporting Information. The linear region of the calibration curve, however, is most convenient since it provides the simplest opportunity for analysis, such as the determination of quinine in commercial tonic water, among others.16 While the enhanced sensitivity offered by fluorescence measurements makes quantitative analysis a standard laboratory activity, the 3D printed fluorometer is useful in exploring other fundamental concepts. A prime example is the investigation of fluorescence quenching mechanisms via simple experiments. Quenching refers to the variety of chemical and physical processes resulting in the reduction of fluorescence intensity. Figure 4b provides evidence for fluorescence quenching of quinine by halide ions. Collisions of the halide ions with quinine in solution facilitates nonradiative transitions to the ground state, thereby reducing the fluorescence signal compared to that of quinine in the absence of halide ions. This collisional, or dynamic, quenching may be described by the Stern−Volmer equation, eq 2.1 This equation holds true for simple cases of collisional quenching, where the concentration of the quenching species (Q) and a Stern−Volmer constant (KSV) are related to the ratio of fluorescence intensities measured in the absence (F0) and presence (F) of the quenching species.
Figure 3. (a) Absorption spectrum (solid blue plot) of 37.0 ppm aqueous [Ru(bpy)3]Cl2 is displayed with an overlay of the emission spectra (dashed blue plot) for a blue (465 nm) LED excitation source. The emission spectrum for a 7.4 ppm aqueous solution of [Ru(bpy)3]Cl2 is shown as a solid orange plot, alongside the profile for the 530 nm cutoff filter employed (dashed black plot). Absorbance data was acquired using a PerkinElmer Lambda 40 UV−vis spectrophotometer, metal complex emission spectrum was obtained employing a PerkinElmer LS 50B luminescence spectrometer, and LED emission spectrum was acquired using an Ocean Optics USB-650 spectrometer. (b) 3D printed filter fluorometer models configured for use with zero (left), one (right), or two (top) optical filters. (c) Standard calibration curve obtained from a 3D printed filter fluorometer for an aqueous solution of [Ru(bpy)3]Cl2 using a 465 nm LED excitation source, 530 nm cutoff filter, and CdS photocell detector.
F0/F = 1 + KSV[Q]
(2)
Data was obtained for the fluorescence quenching of 3.6 ppm quinine in 0.05 M H2SO4 for increasingly concentrated potassium halide salt solutions (KX, where X = Cl−, Br−, and I−). The Stern−Volmer plots displayed in Figure 4b yield linear fits with slopes equal to the Stern−Volmer constant, KSV. As expected, quenching was observed to intensify as the concentration of halide ion increases. Similarly, KSV values derived from the slopes of the linear plots increase in the order of chloride, bromide, and iodide.2 The relative ratios confirm the greater quenching efficiency of bromide and iodide, when compared to chloride.17 This trend correlates well to comparable data sets presented in the literature, where bromide
Cl2 provides an opportunity for students to deliberate and select a proper colored glass cutoff emission filter. Figure 3a shows that a 530 nm cutoff filter provides a simple and inexpensive option for enhancing instrument performance. It is effective in significantly reducing scattered excitation light from reaching the detector. The resulting standard calibration curve for [Ru(bpy)3]Cl2 yields a linear fit from 0.2 to 6.0 ppm (Figure 3c). E
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photographs displayed in Figure 4c confirm that the fluorescence intensity of quinine is quenched with increasing pH, as the dication is deprotonated to the monocation form.18 Inspection or first-derivative analysis of the titration curve reveals a pKa value comparable to that reported in the literature. The utility demonstrated by the 3D printed filter fluorometer is further supported by its use in exploring solvent effects on fluorescence, demonstrations of Rayleigh scattering via nephelometric analysis, and other examples presented in the Supporting Information.
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CONCLUSION Providing increased opportunities for student interaction with analytical instrumentation in significant and diverse ways is an important curricular goal. While the 3D printed filter fluorometer designs presented here are not intended to replace commercial instrumentation, they do provide an inexpensive and versatile set of tools for engaging students at all levels in the exploration of hands-on quantitative analysis. Most significantly, these novel devices allow greater student engagement with instrumentation, as opposed to sharing just one fluorometer across an entire class. These models aim to assist educators in dispelling the “black box” notion of instrument design by empowering students to assemble their own devices. Like our previous work in producing 3D printed colorimeters,13 this report demonstrates that user-friendly and customizable designs provide access to a fundamentally different means of instrument exploration for active learners. While gaining popularity in the research literature, the combination of CAD and 3D printing also offers educators and students a new method for developing innovative designs for the learning laboratory.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00495. Slicer settings, material lists, wiring diagrams, assembly and operation instructions, calibration plots, photographs, and introductory laboratory activity (PDF) Autodesk 123D Design CAD Tutorial (ZIP) Autodesk Inventor CAD Tutorial (ZIP) Example 3D Printing Tutorial (PDF) Autodesk 123D Design CAD and STL files (ZIP) Autodesk Inventor CAD and STL files (ZIP)
Figure 4. (a) Standard calibration curves obtained for quinine in 0.05 M H2SO4 using a 370 nm LED source and CdS photocell detector employing 3D printed filter fluorometer designs for use with (●) both excitation bandpass and emission cutoff glass filters, (▲) only an emission cutoff glass filter, and (■) in the absence of any glass filters. (b) Stern−Volmer plots obtained at room temperature using a 3D printed filter fluorometer (370 nm LED) for the fluorescence quenching of 3.6 ppm quinine in 0.05 M H2SO4 by KX (X = Cl−, Br−, and I−). (c) The pH dependence of the fluorescence signal for 3.6 ppm quinine obtained using a 3D printed filter fluorometer equipped with a 370 nm LED and CdS photocell detector. The inset photo shows the visible change in fluorescent intensity over the same pH range for samples illuminated by a commercially available “black light”.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
and iodide are reported to be approximately 1.5 and 2 times as effective, respectively.16 Dynamic quenching experiments such as these present simple activities that illustrate more advanced level explorations of fundamental excitation−emission phenomena. Fluorometric titration curves are another activity well-suited for the 3D printed filter fluorometer instrument designs reported here. The plot in Figure 4c demonstrates the pH dependence of the fluorescence signal for 3.6 ppm quinine. The quinine samples were buffered at various pH values and excited by a 370 nm LED using a 3D printed filter fluorometer equipped with a CdS detector. Both the plot and inset
Lon A. Porter Jr.: 0000-0002-1092-2776 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully acknowledge financial support of this work by Wabash College and the Department of Chemistry through the Haines Chemistry Fund. The Wabash College 3D Printing and Fabrication Center, supported through a Ball Brothers Foundation Venture Fund Grant, is thanked for F
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facilities and instrumentation support. We are most grateful to Richard F. Dallinger for his expertise and assistance. Wabash College students Mazin H. Hakim, Douglas A. Rourke, and the CHE331 (Advanced Analytical Chemistry) classes are acknowledged for additional instrument testing and feedback.
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REFERENCES
(1) Jameson, D. M. Introduction to Fluorescence; Taylor & Francis: Boca Raton, FL, 2014. (2) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.; Springer: New York, 2011. (3) Wahab, M. F. Fluorescence Spectroscopy in a Shoebox. J. Chem. Educ. 2007, 84 (4), 1308−1312. (4) Algar, W. R.; Massey, M.; Krull, U. J. Assembly of a Modular Fluorimeter and Associated Software: Using LabVIEW in an Advanced Undergraduate Analytical Chemistry Laboratory. J. Chem. Educ. 2009, 86 (1), 68−71. (5) Wigton, B. T.; Chohan, B. S.; McDonald, C.; Johnson, M.; Schunk, D.; Kreuter, R.; Sykes, D. A Portable, Low-Cost, LED Fluorimeter for Middle School, High School, and Undergraduate Chemistry Labs. J. Chem. Educ. 2011, 88 (8), 1182−1187. (6) Wigton, B. T.; Chohan, B. S.; Kreuter, R.; Sykes, D. The Characterization of an Easy-to-Operate Inexpensive Student-Built Fluorimeter. J. Chem. Educ. 2011, 88 (8), 1188−1193. (7) Wang, J. J.; Núñez, J. R. R.; Maxwell, E. J.; Algar, W. R. Build Your Own Photometer: A Guided-Inquiry Experiment To Introduce Analytical Instrumentation. J. Chem. Educ. 2016, 93 (1), 166−171. (8) Scalfani, V. F.; Vaid, T. P. 3D Printed Molecules and Extended Solid Models for Teaching Symmetry and Point Groups. J. Chem. Educ. 2014, 91 (8), 1174−1180. (9) Casas, L.; Estop, E. Virtual and Printed 3D Models for Teaching Crystal Symmetry and Point Groups. J. Chem. Educ. 2015, 92 (8), 1338−1343. (10) Kaliakin, D. S.; Zaari, R. R.; Varganov, S. A. 3D Printed Potential and Free Energy Surfaces for Teaching Fundamental Concepts in Physical Chemistry. J. Chem. Educ. 2015, 92 (12), 2106−2112. (11) Prikryl, J.; Foret, F. Fluorescence Detector for Capillary Separations Fabricated by 3D Printing. Anal. Chem. 2014, 86 (24), 11951−11956. (12) Mendez, J. An Inexpensive 3D Printed Colorimeter. Chem. Educator 2015, 20, 224−226. (13) Porter, L. A., Jr.; Washer, B. M.; Hakim, M. H.; Dallinger, R. F. User-Friendly 3D Printed Colorimeter Models for Student Exploration of Instrument Design and Performance. J. Chem. Educ. 2016, 93 (7), 1305−1309. (14) Grasse, E. K.; Torcasio, M. H.; Smith, A. W. Teaching UV−Vis Spectroscopy with a 3D-Printable Smartphone Spectrophotometer. J. Chem. Educ. 2016, 93 (1), 146−151. (15) Stewart, C.; Giannini, J. Inexpensive, Open Source Epifluorescence Microscopes. J. Chem. Educ. 2016, 93 (7), 1310−1315. (16) O’Reilly, J. E. Fluorescence Experiments with Quinine. J. Chem. Educ. 1975, 52 (9), 610−612. (17) Jayaraman, S.; Verkman, A. S. Quenching Mechanism of Quinolinium-Type Chloride-Sensitive Fluorescent Indicators. Biophys. Chem. 2000, 85 (1), 49−57. (18) Schulman, S. G.; Threatte, R. M.; Capomacchia, A. C.; Paul, W. L. Fluorescence of 6-Methoxyquinoline, Quinine, and Quinidine in Aqueous Media. J. Pharm. Sci. 1974, 63 (6), 876−880.
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