Building a Raman spectrometer…

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Discussion Overview

The discussion revolves around the construction of a Raman spectrometer, particularly using Arduino technology as an alternative to previous Raspberry Pi designs. Participants explore the feasibility of creating a portable device for drug identification, the differences between Raman and mass spectroscopy, and the technical challenges involved in building such a device.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants discuss the potential of Arduino as a more practical alternative for building a Raman spectrometer compared to Raspberry Pi, which had limitations in mobility and usability.
  • There is mention of existing handheld scanners used by customs, prompting inquiries into their operational principles.
  • Participants express confusion regarding the integration of Raman spectroscopy with mass spectroscopy, emphasizing that they are distinct techniques requiring different hardware.
  • Clarifications are made about the technical processes involved in both Raman and mass spectroscopy, highlighting their differences and the challenges of each method.
  • Some participants share insights on the cost differences between commercial spectrometers and DIY options, noting the significant price reduction.
  • There are discussions about power supply requirements for DIY spectrometer projects, with participants sharing their experiences and solutions for powering devices.
  • One participant expresses a desire for guidance and acknowledges their learning process while working on the project.

Areas of Agreement / Disagreement

Participants generally agree on the distinction between Raman and mass spectroscopy, but there is no consensus on the best approach for building a portable Raman spectrometer or the specifics of power supply requirements. The discussion remains unresolved regarding the integration of different spectroscopic techniques and the practicalities of DIY construction.

Contextual Notes

Participants note the challenges of understanding voltage requirements and the reliability of using resistors for powering devices, indicating a need for clearer guidelines in DIY electronics.

Who May Find This Useful

This discussion may be useful for hobbyists, students, and professionals interested in DIY spectroscopy projects, particularly those exploring the use of Arduino technology in analytical chemistry.

  • #31
sbrothy said:
Your wife has no comments on that? :woot:
She mainly knows about the fire at home (at our old apartment years ago), and we laugh about it now. It involved a HAM radio project (we are both HAMs), where I made a fundamental mistake in building a large battery backup box. That was embarrassing...
 
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  • #32
berkeman said:
She mainly knows about the fire at home (at our old apartment years ago), and we laugh about it now. It involved a HAM radio project (we are both HAMs), where I made a fundamental mistake in building a large battery backup box. That was embarrassing...
Eeesh! :smile:
 
  • #33
The original paper (including the "Supporting Information") is a little silent on the nature of the lenses. I'd like to analyze my beam using a laser beam profiler but that darn thing is even more expensive than the spectrometer itself. I could build it myself but where will I end up having to build gizmo after gizmo?

I hope I understand that the long pass filter is supposed to filter out the Rayleigh radiation and as such is a pretty straightforward acqusition. The lenses om the other hand....

I've come to understand that I need biconvex lenses as the beam has to go back and forth through it. but their exact nature still eludes me a little. Can I just "try" with what I think are the proper ones, or do I need to profile the beam and "math it out"? The example I'm trying to follow uses a cube beam splitter (splitting the beam 70%/30%) but I'm wondering whether it wouldn't be smarter using a "proper" beam splitter?

Incidentally, I found this, related, document:

The Design and Construction of an Affordable Raman Spectrometer.
 
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  • #34
Well, actually doing my homework myself and understanding the difference between "cut-off" and "cut-on" filters I realize I need a "cut-off" filter blocking wavelengths longer than 550nm in order to cut off Rayleigh scattering radiation.

I'm surprised about the prices of these lenses though! Cheap they aren't! I read somewhere one can use ordinary magnifying glasses instead of biconvex lenses, but I doubt that works for laser light though.
 
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  • #35
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  • #37
sbrothy said:
OK, after using my own brain and search skills I think I found the correct long-pass filter (no affiliation of course):

https://www.thorlabs.com/thorProduct.cfm?partNumber=FGL550S

Although I think I need an uncolored one.

and the lenses:

https://www.thorlabs.com/search/thorsearch.cfm?search=biconvex+lens+laser

Just need to find out which coating I need, if any.

I must admit I'm surprised that the filter and lenses are the most expensive part of this project!

Well, it turns out I “need” the colored one after all. At least that’s what they use in the paper I’m using as a guide.

Again, I’m in no way affiliated with Thorlabs. They just seem to have most of what I need, albeit, as I mentioned, they have no scruples charging you. In fact, they also have a complete Raman Spectrometer Kit.

Again, cheap it is not.
 
  • #38
I bought My engineer partner in this bought this SparkFun Triad Spectroscopy Sensor - AS7265x (Qwiic) but I think this was a mistake (and the blame for this is mine as he did it on my request). It can do 3 different types of spectroscopy, but none of them is really what I need. It may turn out to be useful anyway though.

Details here:

https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/697/SEN-15050_Web.pdf

EDIT: Fun fact: as dimensions are difficult to assess I thought it was 10x10 cm, but it turned out to be 2x2 cm!

82829E37-3A3D-474E-8139-B9E1BA785CD9.webp
 
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  • #39
I bragged about not going down on equipment and then I stumbled across this guy’s blog.

I must admit I feel like I’m missing something here now.

Also, just ftr I should mention that my engineer partner bought the triad board (on my wrong request). I better find something constructive to use it for now! :smile:
 
  • #40
A DIY spectrometer for harm reduction is an incredible, life-saving goal. The biggest challenge will be ensuring clean, reproducible spectra from that weak Raman scattering. Good luck overcoming the technical hurdles. I'll be following your updates!
 
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  • #41
Thank you for the kind words. As you say it's gonna be an uphill battle.

EDIT: I know this is inanely weak but I couldn't resist: It's gonna be like the attack of the laser light brigade. (I'm really sorry!)

Almost incidentally, it occurs to me that the SparkFun Triad Spectroscopy Sensor - AS7265x (Qwiic) could perhaps be used to build a makeshift pulse oximeter measuring the SpO2 of someone under the influence of drugs reducing the oxygen intake.

They're probably not voluntarily gonna make me measure it, and if they already have blue lips the SpO2 probably isn't the most important variable. It's in the scenario ballpark though and it's something productive to use the board for! :woot:
 
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  • #42
BTW, all my rambling about power adapters and batteries in the beginning of this thread was because I didn't understand the Arduino yet. Everything I need is provided by that one board via a USB connection to the computer. Onboard power outlets and whatnot for a multitude of purposes. I'm quite impressed with the thing.

So yes, the Raspberry and the Arduino are two very different "creatures".
 
  • #43
Welp, I had hoped that I could've skimped my way through this and just follow the instructions from some howto - like building a LEGO DUPLO model - but it seems I'm actually going to work for it! This means I'm not getting around profiling my laser beam and actually use some mathematics!

EDIT: Not to mention actually understanding Raman-scattering! I'm completely flabbergasted (and a little outraged)!

Darn!

:woot:
 
  • #45
This project is slowly getting more and more expensive. It's beginning to look like something I'll do solely for the challenge. For the knife edge profiler it looks like I need a motorized stager with micrometer accuracy.

It doesn't look like they come cheap.

:frown:
 
  • #46
Seems I was a little pessimistic. It wasn't as expensive as I feared. I've ordered a stepper (hope I got the right resolution but if not it was only $20 so it isn't the end of the world) and an Arduino interface for it. Also a photodiode.

Let's see if it turns up. I'm continuously ordering and receiving all kinds of stuff, most of which I have no use for but at some point I must end up with something useful....
 
  • #47
So, I've bought a bunch of stuff which I hope will prove helpful in building the laser profiler and some that will fit with the multipurpose spectroscopy card, as it can't just sit there without doing some good. Especially not at that price. Specifically this gizmo:

SparkFun Serial Basic Breakout - CH340G

I bought a 100mW laser which the ad said can cut stuff(?), and yes, I know it doesn't make much sense. I was a litte inebriated and added it to my order before the absurdity dawned upon me. It made the shipping free though, didn't cost much, and anyway you can never get enough lasers!

I also bought some stepper motors. One of them pretty random but the other one I'm reasonably sure can be used for the laser profiler:

Stepper Motor - 32 oz.in (200 steps/rev, 1200mm Wire)

I also ordered a "3.3V-5V 3PIN Photodiode Module LM393 Light Sensor Switch Module for Arduino Raspberry Pi Photosensitive Diode Detection Switch"

As always: No affiliation.

EDIT: Heh, silly little fact: without physical or mechanical schooling it took me a little while to wrap my head around what the lead in leadscrew referred to. Must admit I initially was a little nonplussed as to why this screw had to be lead (as in the element)(?)! o0)
 
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  • #48
sbrothy said:
...I was a litte inebriated and added it to my order before the absurdity dawned upon me. It made the shipping free though, didn't cost much, and anyway you can never get enough lasers!

If you drink, don't shop.
 
  • #49
Hah yeah, good advice. I said "a little inebriated" though, not blasted. And my purchase did make sense. As I said I had to buy one thing more to make shipping free and it was pretty cheap.

EDIT: A backup laser is probably a good idea. Some other day I'll be bombed out of my skull and connect the wires incorrectly shorting the current laser. (Or loose my sight trying to secure it actually works!) I'm joking
 
  • #50
OK. Got my stepper motor. And a serial card for the triad spectroscopy card. I’m not sure it’s the correct one, but I’m moving forward. Or at least I’m moving in some direction… :woot:
 

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  • #51
The more I read about the Sparkfun Triad Spectroscopy Sensor the more impressed I am. To the point that I'm wondering if I need Raman spectroscopy at all.

Interfacing Triad Spectroscopy Sensor as7265x with Arduino.

Not that I'm backing down. I'm committed to building the laser profiler. I just wonder. I need to test the limits of that Triad thingy.

EDIT: And yes, the Sparkfun Triad board is a playtoy with simply reflects light off stuff. It's not for chemical analysism however fun it might be to irradiate a banana.
 
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  • #52
So time to get serious.

If anyone disagree with any of the following please speak now or forever hold you silence. :woot:

All this 532 nm green laser stuff looked good on the surface but as it turns out the optimal choice seems to be a 785 nm (near-IR) laser. Specifically because it reduces fluorescence. I don't intend to make it a handheld device. If I buy from a reputable source I might be able to skip some of the profiling...
 
  • #53
There seems to be a range of NIR drug spectrometers within price-range of "ordinary" people. Also these are within DIY yourself range. We're still talking Raman spectroscopy just in the range of 785-1064 nanometers and so obviously more expensive.

On-site illicit-drug detection with an integrated near-infrared spectral sensor: A proof of concept

Illicit-drug production, trafficking and seizures are on an all-time high. This consequently raises pressure on investigative authorities to provide rapid forensic results to assist law enforcement and legal processes in drug-related cases. Ideally, every police officer is equipped with a detector to reliably perform drug testing directly at the incident scene. Such a detector should preferably be small, portable, inexpensive and shock-resistant but should also provide sufficient selectivity to prevent erroneous identifications. This study explores the concept of on-site drugs-of-abuse detection using a 1.8 × 2.2 mm2 multipixel near-infrared (NIR) spectral sensor that potentially can be integrated into a smartphone. This integrated sensor, based on an InGaAs-on-silicon technology, exploits an array of resonant-cavity enhanced photodetectors without any moving parts. A 100% correct classification of 11 common illicit drugs, pharmaceuticals and adulterants was achieved by chemometric modelling of the response of 15 wavelength-specific pixels. The performance on actual forensic casework was investigated on 246 cocaine-suspected powders and 39 MDMA-suspected ecstasy tablets yielding an over 90% correct classification in both cases. These findings show that presumptive drug testing by miniaturized spectral sensors is a promising development ultimately paving the way for a fully integrated drug-sensor in mobile communication devices used by law enforcement.
 
  • #54
So, I've entered into dialogues with companies asking questions like this:

I'm trying to build a Raman spectrometer. I need a non-polarizing, UV-grade fused silica dichroic square cut piece of a microscopic slide (25 mm × 25 mm × 1 mm) for a 532nm laser, which, when kept at 45° to the excitation light path, yields a reflection/transmission ratio of 30:70. I'm working with a spectral range of 200–2000 cm⁻¹. In particular I'm using this document: "Fabricating a Low-Cost Raman Spectrometer to Introduce Students to Spectroscopy Basics and Applied Instrument Design" (Cite: J. Chem. Educ. 2021, 98, 2109−2116) as a reference and I'm interesting in further components if you can supply them too. Within a reasonable price range that is. I'm dealing on behalf of my own Danish company. Any advice is also welcome. This is a proof-of-concept project, so this may well be the first in a series. I'm planning on upgrading to Raman NIR spectroscopy should this project be a success.

If you can find any holes in my reasoning (which I expect) any comments are welcome. I'm planning on buying the laser from a reputable company too so I don't have to profile it.
 
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